本文采用倾向得分匹配和双重差分方法系统评估了对外直接投资对中国高科技企业全要素生产率的平均效应和动态效应，并从投资特征视角分析了OFDI生产率效应的差异性。结论表明：（1）对外直接投资显著促进了高科技企业全要素生产率的提升，且促进作用呈现先上升后下降的趋势；（2）绿地投资对高科技企业TFP的促进作用具有滞后性，而跨国并购对当期和多期TFP均产生积极作用；（3）技术寻求型OFDI对高科技企业TFP的促进作用最为显著，当地生产型OFDI的生产率效应具有滞后性，而商贸服务OFDI的生产率效应并不显著；（4）在高收入水平国家（地区）投资能够显著提升企业全要素生产率，在中低收入国家（地区）投资对企业TFP的作用并不显著。上述研究为高科技企业理性选择对外投资策略提供科学依据。

   China′s high-tech enterprises are climbing to the high-end link of the global value chain, so they need to improve their innovation ability and total factor productivity in order to enhance their position in the international division of labor system. Due to the rapid change of knowledge, high-tech enterprises rely on their own resources to carry out high-cost innovation activities, which has been difficult to adapt to the increasingly fierce international competition. High tech enterprises can obtain strategic assets such as advanced technology, professional talents, sales channels and management experience through foreign direct investment, improve the position of global value chain, and drive the transformation and upgrading of domestic industries. 
   Based on the existing research, this paper extended the following viewpoints: first, using PSM and did methods to systematically estimate the productivity effect of Chinese high-tech enterprises′ FDI. At present, there is no systematic evaluation of the micro performance of foreign investment of high-tech enterprises. In the past, case analysis, event study and regression analysis were used to study the investment performance of high-tech enterprises. In this paper, by constructing the database of China′s high-tech enterprises′ foreign direct investment in 2008-2015 and adopting the double difference method based on tendency score matching, the grouping effect of FDI enterprises and non-FDI enterprises, the foreign direct investment, and the time effect of the two periods were controlled, and then the net effect of FDI on TFP was studied. The research method effectively controls the endogenous problems caused by sample selection bias and missing variables in the regression process, so as to more accurately identify the causal relationship between FDI and productivity of high-tech enterprises, and ensure the reliability of the research conclusions. Secondly, this paper investigates not only the average effect of OFDI on TFP of high-tech enterprises, but also the dynamic effect of OFDI on TFP of high-tech enterprises. Thirdly, group estimation is made according to investment mode, investment motivation and income level of host country, and the difference of productivity effect of OFDI was investigated from the perspective of investment characteristics. 
    The conclusion shows that: (1) Foreign direct investment has significantly promoted the total factor productivity of high-tech enterprises, and the promotion effect shows a trend of rising first and then declining; (2) Green land investment has a lag effect on the promotion of high-tech enterprises′ TFP, while cross-border M&A has a positive effect on the current and multi-stage TFP. The construction cycle of green space investment is relatively long, and it needs to bear the external integration cost to adapt to the market environment of the host country, which leads to the current productivity effect of green space investment is not significant. With the enterprises gradually embedded in the local production system and knowledge network, the productivity effect of green investment can gradually appear. Through the merger and acquisition of foreign enterprises with specific advantages, Chinese high-tech enterprises can quickly form complementary advantages with the unique knowledge, technology, brand, management experience and other strategic assets of the target enterprises, so as to improve the production efficiency of enterprises and their position in the global value chain; (3) Technology seeking OFDI has the most significant promotion effect on the TFP of high-tech enterprises. The productivity effect of OFDI is lagging behind, but the productivity effect of OFDI is not significant. Technology seeking OFDI is an important way for Chinese high-tech enterprises to adapt to the trend of R&D internationalization and build global R&D system. Enterprises acquire knowledge assets, human capital and cutting-edge technology by establishing R&D institutions, establishing green investment methods such as science and technology parks, as well as mergers and acquisitions of technology leading enterprises. Therefore, this way of acquiring reverse technology spillovers is the most direct and its sustained effect is more obvious; (4) Investment in high-income countries (regions) can significantly improve the production efficiency of enterprises, while investment in low-income countries (regions) cannot significantly improve the production efficiency of enterprises. The investment of enterprises in high-income countries (regions) in emerging market countries can be closer to leading technologies and products, and learn more efficient management mode, so as to improve their own production efficiency.
    The above research provides scientific basis for the rational choice of foreign investment strategy for high-tech enterprises. First, high-tech enterprises need to choose the best market entry strategy in combination with their own strategic orientation. After the financial crisis, more and more high-tech enterprises have invested in the United States, Germany, the United Kingdom and other developed countries to obtain creative assets such as technology and knowledge. However, to obtain reverse technology spillovers, enterprises need to have strong knowledge accumulation, innovation and management capabilities to effectively integrate knowledge assets. Secondly, the government should further improve the overseas investment system and platform construction to provide important support for high-tech enterprises to deeply participate in the international industrial division system. At present, a significant feature of OFDI of high-tech enterprises in China is to move forward to the upstream of the global value chain and gain advanced technology, brand and overseas market management experience through cross-border M&A. We should encourage enterprises to set up research centers or laboratories, international technology transfer institutions and science and technology parks in developed countries such as the United States and the European Union by improving policy support, setting up funds, focusing on cultivation and guidance, and optimizing intermediary services, so as to promote advantageous enterprises to build a global R&D network and enhance the status of the global value chain. Finally, we will improve the multi-level bilateral and multilateral cooperation mechanisms. The investment goal of high-tech enterprises is to obtain high value-added resources such as advanced technology and marketing network, so to achieve the high-end of the value chain. Therefore, they are more likely to face various risks such as technical standard barriers, intellectual property litigation, national security review, etc. Bilateral or multilateral industrial investment cooperation funds can be set up to provide financial support for the development and investment of key industries among countries. In view of some outstanding problems such as weak recognition of China′s technical standards in some countries, we should strengthen the protection of intellectual property rights, coordinate the technical standards with countries along the line, promote the signing of mutual recognition agreements on technical standards, and reduce the risk of enterprises being rejected by the local market due to technical standards.