Abstract:    Innovation performance improvement is an important issue for corporate sustainable development. The existing research has preliminarily constructed a research framework among internal knowledge creation system, external knowledge acquisition system and innovation performance. While internal knowledge creation system mainly explores the relevant problems about absorptive capacity, like creating and generating new knowledge, external knowledge acquisition system cares more about R&D cooperation which is performed by the company and other external organizations. There is a pity that external knowledge acquisition system ignores the roles of enterprise export activities, which are also important methods to acquire external knowledge. Enterprises can get comprehensive external knowledge which is transferred in the external knowledge flow network, thus promoting innovation performance. Serving as the approach to contacting external knowledge, export activities and R&D cooperation are of great importance. As a result, enterprise export activities should be brought into the external knowledge acquisition system, and the relationship between export activities and innovation performance should be explored further, which is scarcely studied in the developing countries at present.This paper attempts to incorporate export factors into the enterprise external activities knowledge acquisition system, extend the research framework of innovation performance, and explore the relationship between enterprise export activities, R&D cooperation, absorptive capacity and innovation performance. Therefore, this paper proposes six hypotheses: Hypothesis 1 is that R&D cooperation has a positive impact on absorptive capacity; Hypothesis 2 is that R&D cooperation has a positive impact on innovation performance; Hypothesis 3 is that absorptive capacity has a positive impact on innovation performance; Hypothesis 4a is that absorption capacity has a positive impact on export activities; Hypothesis 4b is that export activity has a positive impact on absorptive capacity; Hypothesis 5 is that export activity has a positive impact on innovation performance; Hypothesis 6 is that export activity has positive impact for R&D cooperation. Data in this paper comes from the database in listed companies of China′s high-tech enterprises，from which we finally chose 209 high-tech enterprises as the research sample. Then, R&D cooperation information of the above 209 companies are manually collected. The hypothesis is verified using the structural equation model. The research results show that: (1) Enterprise absorptive capacity is an important factor to promote the innovation performance. Absorptive capacity not only has a direct positive impact on the innovation performance, but also has an intermediary role in the positive impact of export activities and R&D cooperation on firm innovation performance. (2) Export activities have direct positive impact on R&D cooperation and innovation performance. The foreign market environment can help enterprises to enhance their innovation ability and innovation performance, also promote to establish R&D partnerships with foreign excellent enterprises or scientific research institutions. (3) Enterprises with higher absorptive capacity can promote enterprises to expand export activities, and their strong absorptive capacity in export activities can help enterprises to acquire and absorb foreign knowledge resources and further promote the absorption capacity. (4) There is a "virtuous circle" among R&D cooperation, absorption capacity and export activities. R&D cooperation enhances the absorption capacity of enterprises and further promotes enterprise exports; on the other hand, export activities will enhance opportunities for establishing cooperative relationships with external partners, thereby promoting R&D cooperation.This paper mainly contributes to the area in the following aspects: First, in theory, the research framework of innovation performance is extended. Besides the direct relationships among R&D cooperation, innovation performance, export activities and absorptive capacity, the intermediary role of absorptive capacity and export activities are also explored. Second, all of our findings reveal the contribution of improving absorptive capacity and export activities of innovation performance.The conclusions of this paper have the following enlightenment for the improvement of innovation performance of high-tech enterprises: First, improve the absorption capacity of enterprises. In terms of manpower construction, enterprises should attract high-level research personnel to supplement the enterprise scientific research personnel pool, establish a knowledge management system to promote internal knowledge flow, and enhance the ability of employees and organizations to acquire, digest and absorb new knowledge. In terms of technical capabilities, enterprises should strengthen R&D investment, promote the integration of new and old knowledge, enhance the technology development capability and independent innovation capability of enterprises, and promote the knowledge flow cycle between prior knowledge and absorptive capacity. Second, expand the breadth of R&D partners. Enterprises should actively cooperate with domestic customers, suppliers, competitors, universities and research institutes to build a long-term and stable R&D partnership with multiple parties. In addition, enterprises should establish cooperative and innovative partnerships with organizations in the EU, the United States and other countries and regions, and builds a platform for knowledge exchange and exchange of multinational enterprises, absorbs high-quality knowledge resources from abroad, expands the enterprise knowledge base, and promotes the absorption capacity and innovation performance. Create an international industrial park, establish a multi-dimensional and prominent international innovation collaboration platform, accurately connect with foreign high-quality innovation resources, and innovative interaction and technology sharing. The government should create a good policy environment for enterprises to cooperate with university and scientific research institutions, and build an online information docking platform, guide the establishment of a resource sharing mechanism, and promote the open sharing of innovation elements. The government should learn from Israel′s relevant experience, then build a joint committee of innovation and cooperation among countries to achieve complementary advantages, resource connectivity and multi-win. Third, enrich the internationalization activities of enterprises. Enterprises should enhance the level and quality of export products, diversify the export market continuously, focus on developing Europe and emerging markets. Promoting the improvement of innovation ability by acquiring foreign high-quality resources and improving a high level of transnational R&D cooperation through high-quality export trade activities, the enterprises can upgrade the innovation performance. Fourth, establish overseas R&D cooperation centers. Establishing overseas R&D cooperation platforms and communication centers by various export trade activities, scientific research personnel exchange and technology introduction could be realized. The government should help build a high-level enterprise cross-border exchange platform, build a dynamic information service consulting platform, and provide practical services for the internationalization of enterprises.

Key words: export activities, absorptive capacity, R&D cooperation, innovation performance