Abstract:     The national high-tech zone is a key carrier for China to implement efficient innovation, attract international innovation resources and elements, and develop high-tech industries. In 2019, the actual amount of FDI attracted by enterprises in the high-tech zone reached 382.76 billion yuan in RMB, accounting for 40.7% of the country′s total (941.5 billion yuan).It has become the main force for China to learn from global innovation and obtain economic resources, and it plays an important role in the construction of domestic and international dual-cycle development pattern.
    At present, China is in a critical period of accelerating innovation-driven development, and the national high-tech zone is an important carrier to promote innovation development. Therefore, to clearly understand the role of FDI is the key to strengthen the international circulation and realize the effective allocation of international resources and elements，which has important theoretical and practical significance for promoting the high-quality development of national high-tech zones.
    Currently, only a few studies have focused on the impact of FDI on the production efficiency and technology spillovers of national high-tech zones, while other studies pay attention to their performance evaluation and related factors. These research results all indicate that FDI can have an impact on the production or technical efficiency of national high-tech zones through knowledge or technology spillovers. However, these studies generally only analyze from the perspective of FDI quantity, and do not systematically and deeply analyze whether the mechanism of FDI on the innovation performance of national high-tech zones is affected by the high-tech zone′s own knowledge or technological level.
    Based on the panel data of 52 national high-tech zones in China from 2008 to 2018, this paper analyzes the impact of FDI quantity and FDI quality on the innovation performance using the knowledge accumulation as the threshold variable via the Hansen nonlinear panel threshold regression model. The research results show that there is a complex nonlinear relationship between FDI quantity and quality and the innovation performance. When the level of knowledge accumulation is lower than the threshold 1, FDI quantity has a significant positive impact on the innovation performance of high-tech zones, that is, it can significantly improve their innovation performance. While the level of knowledge accumulation exceeds threshold 1, the impact of the FDI quantity on the innovation performance is no longer obvious. When the level of knowledge accumulation is below the threshold 1, the FDI quality has a significant negative impact on the innovation performance; while the former exceeds the threshold 1, the latter has an obvious positive impact on the innovation performance. When the former exceeds the threshold 2, the marginal effect of the positive impact of the FDI quality is further enhanced, that is, improving the FDI structure and quality can significantly upgrade the innovation performance of the national high-tech zone. These research results provide a theoretical reference for the national high-tech zone to achieve high-quality development.
    Combined with these research conclusions, three policy recommendations are put forward: firstly, in light of the high-quality development policy of the national high-tech zone, it is necessary to formulate new FDI introduction policies and screening systems that focus on FDI quality, and encourage enterprises in high-tech zones to actively integrate global high-level innovative resources and elements to achieve high-quality development. The second is to further improve the knowledge accumulation level of the high-tech zone and lay the foundation for the integration of global high-quality innovation resources. That is to say, with high-tech enterprises as the main body, it needs to increase the intensity of talent attraction and training, especially high-level talents. Meanwhile, it needs to increase and optimize science and technology investment, promote enterprises to carry out high-quality R&D and innovation activities. With the improvement of the knowledge accumulation level of enterprises, the ability of the high-tech zone to integrate global innovation resources has finally been improved.

Key words: FDI quantity, FDI quality, knowledge accumulation, innovation performance