Abstract:    Over the past 40 years of reform and opening up, the strategies of "Bringing in" and "Going out" have made remarkable achievements, which attract the investments of whole global capital flowing into China with enthusiasm. According to statistics, in 2016, the flow of foreign direct investment (FDI) into China exceeded 130 billion US dollars, with a record high scale. While Chinese enterprises have obviously accelerated their outward foreign direct investment (OFDI) simultaneously, and the scale of OFDI in 2016 is near 200 billion US dollars, with significant increase. The central economic work conference put forward that, the construction of "the Belt and Road" should be emphasized, and "Bringing in" and "Going out" are dual important, the strategies are beneficial to promote innovation through investment cooperation. The questions are, what kind of innovation spillover influence does "Bringing in" and "Going out" display in China new era? How is the relationship in the process of coexistence and development of FDI and OFDI, are they competition with suppression or mutual integration with promotion? And how to speed up the innovative country construction in China new era with the profits of innovation spillover during capital dual flow? These questions have important research value and practical significance.
    The existing literatures on innovation spillovers of capital flows are mostly confined to a single FDI perspective or a single OFDI perspective, ignore the symbiotic evolution characteristics of "Bringing in" and "Going out". In China′s new era, the opening of the financial market will be speeded up, and the construction of "the Belt and Road" will be promoted, it is significant to welcome "Bringing in", while "Going out" becomes enthusiastic and optimistic, which reveals dual capital flow characteristics of FDI and OFDI. Under this evolutionary trend, the impact of "Bringing in" and "Going out" on technology innovation may have iterative effects: on the one hand, because of economic development and industrial upgrading, simple manufacturing industries may lose the driving force of technology innovation, it is necessary to raise the technical threshold of foreign direct investment, leverage the Chinese enterprises innovation foundation of "Going out" by FDI technology spillover. On the other hand, Chinese enterprises have absorbed foreign R&D experience during "Going out", introduced advanced technology and enhanced innovation capability, which would force foreign enterprises to improve the technological competition level during the investment into China market, it could boost FDI innovation spillover through OFDI reversely. 
    In views of the above analysis, the paper broke through the limitation of single analysis perspective, studied the innovation spillover effects of China′s capital flows from the perspective of dual symbiosis of "Bringing in" and "Going out" systematically. Firstly, it tested and judged the single dynamic innovation spillover effects of FDI or OFDI in China; secondly, considering the possible interactive affection between FDI and OFDI, it studied the innovation spillover effects of FDI under the constraints of OFDI, as well as, it discussed the OFDI innovation spillover effect under the influence of FDI. Thirdly, it studied the spatial heterogeneity of the interactive innovation spillover effect of dual capital flow according to the economic geography differences of the eastern, central and Western regions in China.
    The results showed that, FDI has a dynamic restraining effect on regional innovation, while OFDI′s innovation spillover shows the characteristics of "U" shape triple threshold, which promotes regional innovation in prominent level. Meanwhile, there is a significant interactive innovation spillover effect between "Bringing in" and "Going out", high-intensity OFDI could reverse the inhibition of FDI innovation spillover, while specific-intensity FDI could maximize OFDI innovation spillover. Further research also finds that, there is significant spatial heterogeneity in the interactive innovation spillover effect of dual capital flow in China, high-intensity OFDI is beneficial to reverse the inhibition of FDI innovation spillover in eastern regions, but it does not happen in other regions, FDI in eastern regions could positively regulate the innovation spillover effect of OFDI, while excessive high-intensity FDI weakens or even inhibits OFDI innovation spillover in central regions and western regions.
    The main policy implications of the paper are as follows, in the symbiotic interactive stage of dual capital flow, the relationship between "Bringing in" and "Going out" is not simple equal, they should be adjusted hierarchically and scientifically, and stimulate the innovation spillover effect of dual capital flow systematically. (1) There is obvious technology inhibition during foreign enterprises investing in China currently, and it is invalid for low technology FDI to stimulate innovation spillover at present, therefore local governments should not absorb FDI only for simple achievements but ignore the technology threshold, they should emphasize on upgrading technical threshold of "Bringing in", promote regional innovation by introducing technological models. (2) Low level outward investment is invalid to stimulate OFDI innovation spillover profits, and primary external expansion will inhibit the enthusiasm of domestic technology innovation, with the inspiration of "the Belt and Road" construction, Chinese enterprises should take the initiative of "Going out" to seek the external technological potential progress in developed countries and regions, and siphon to enhance domestic innovation capability. (3) Capital dual flow has complex interactive innovation spillover effects, consequently, "Bringing in" should not abandoned unilaterally, or only emphasize on "Going out", the regional governments should upgrade the technical threshold of foreign enterprises investment with the competition of technical progress during OFDI, which could stimulate positive innovation spillover of FDI. Meanwhile, foreign enterprises investment strategies should be adjusted and optimized dynamically, which is to maximize OFDI innovation spillover by FDI regulation. (4) The spatial heterogeneity of interactive innovation spillover effects of capital dual flow should not be ignored. The eastern regions have better innovation foundation and human resources, FDI and OFDI are both conducive to enhancing regional innovation capability in high intensity, "Bringing in" and "Going out" should be encouraged equally. The innovation activities in central regions are sensitive to the interactive innovation spillover effects of "Bringing in" and "Going out", they should implement dual adjustment of FDI and OFDI, and avoid falling into innovation inhibition of capital flow. The industrial foundation and innovation capability in the western regions are relatively low, and the innovation spillover contribution of "Bringing in" is insufficient, but it could release the technology spillover of "Going out", which is beneficial to feed back its domestic innovation capability.

Key words: FDI, OFDI, innovation efficiency, threshold effect