Abstract: Nowadays, China′s economy development model has been transforming from the high growth driven by investment to the high-quality development driven by factors. In the process of realizing rational allocation of factor resources, the innovation upgrading has become the primary driving power for the high-quality development. At the same time, the Belt and Road Initiative aims to further deepen enterprises′ going global and bringing in strategies, promote enterprises′ outward foreign direct investment, and optimize the enterprises′ transformation upgrade, since it was put forward. From 2013 to 2018, China′s outbound non-financial direct investment flows have increased from US $92.74 billion to US $120.5 billion. In 2018, non-financial direct investment to countries along the Belt and Road Initiative reached US $15.64 billion, rising by 8.9% year-on-year. Therefore, while the Belt and Road Initiative could promote the transformation of domestic industrial structure and the enterprises′ innovation upgrading, it would play a crucial role in the realization of the high-quality development in China.
     At the same time, the paper uses the methods of the Propensity Score Matching and Difference-in-Difference to evaluate the impact of the Belt and Road Initiative on the enterprises′ innovation upgrading. The explained variable is the enterprises′ innovation upgrading, and the core explanatory variable is the Belt and Road Initiative. The result shows that the Belt and Road Initiative has significantly improved the quantity and quality of the enterprises′ patents, and further promoted the innovation upgrading of the enterprises. Simultaneously, the results remain unchanged when it controls the variables, such as enterprises′ productivity, scale, age, cash flows, leverage ratios and profit margins. Especially, the dynamic effect test further shows that the promotional effects are stronger than before in the third-year and fourth-year. In addition, the robustness tests are still robust, including the panel instrument variables, replacing the explained variables, triple-difference methods and the continuous panel data.
   One one hand, the paper further analyzes the heterogeneity of enterprises′ innovation upgrading from the two dimensions of the space and industry, including the region ,the ownership and the industry type. The heterogeneity results are as follows. First of all, whether the enterprises are located in the region along the initiative provinces or not, it has significantly promoted the innovation upgrading of the enterprises in the region. Meanwhile, for the enterprises′ ownership, the initiative mainly exists on the state-owned enterprises′ innovation upgrading. Lastly, in terms of the industry type, the initiative mainly promotes the mature industrial enterprises′ innovation upgrading.
    One the other hand, the Belt and Road Initiative mainly through the four mechanisms to promote the enterprises′ innovation upgrading, respectively the market competitiveness, the R&D, the enterprises′ financial constraints, and the rise of the value chain. The specific paths are as follows. Firstly, for the market competitiveness, the Belt and Road Initiative could help Chinese companies to get closer to the destination country. So that they could acquire more overseas operating revenue to expand their scale. Secondly, for the enterprises′ R&D, the Belt and Road Initiative could encourage the enterprises to set up R&D centers, and acquire advanced technical knowledge and skill resources in the host countries. Thirdly, for the financial constraints, the Belt and Road Initiative could reduce the external risks of the information asymmetry, and further put the reduced cost into an more effective domestic investment. Fourthly, for the global value chain, the Belt and Road Initiative could promote the enterprises to produce high value-added products, improve the height of the value chain, enhance the intellectual property technology innovation, and ultimately promote the enterprises′ innovation upgrading.
    Based on the conclusions above, the research result further provides some practical references to the enterprises′ innovation upgrading under the Belt and Road Initiative. Primarily, the Chinese government should strengthen strategic cooperation and create a community of interests with the countries along the Belt and Road Initiative. Secondly, local governments should participate in the Belt and Road Initiative and encourage local enterprises to invest the countries along the Belt and Road Initiative. Finally, Chinese enterprises should integrate into the Belt and Road Initiative. At last, this paper finds that the Belt and Road Initiative accelerates the enterprises′ outward foreign direct investment and ultimately promotes the innovation upgrading.

Key words: Belt and Road Initiative, innovation upgrading, difference-in-difference