As one of the important ways of achieving high-level opening-up to the outside world, the policies of bringing in and going out have not only brought Chinas economic prosperity, but also had an important impact on the environment. However, the research on the environmental effect of two-way FDI synergy is still not sufficient, and the specific channels of impact need to be further clarified. Based on the data of 30 provincial-level administrative regions in Chinas mainland from 2003 to 2018, this paper first introduced the capacity coupling system model to measure the level of two-way FDI synergy, and then matched the data of PM2.5 pollution, technological innovation and other data to explore the environmental effects and action path of two-way FDI synergy. The study found that: Two-way FDI synergy had significant inhibitory effect on local environmental pollution, and under the influence of spatial autocorrelation, the environmental improvement effect was still significant after the environmental pollution levels of other regions were included in the analysis. The environmental promotion effect of two-way FDI synergy had a positive spatial spillover effect, which could radiate to other regions and drive the improvement of environmental quality of these regions. Further research showed that the effect of two-way FDI synergy on environmental pollution mitigation had regional heterogeneity, especially in the inland and less polluted areas. Two-way FDI synergy could aggravate the regional environmental pollution by inhibiting the ability of imitative innovation, and could alleviate the pressure of environmental pollution by improving the level of independent innovation. The improvement of independent innovation capability was a long-term solution to giving full play to the positive environmental effect of two-way FDI synergy. Although imitative innovation played a positive role in the initial stage, with the continuous increase of expenditure on imitative innovation, the environmental improvement effect tended to decline. Based on the above conclusions, it is proposed that economic and environmental policies should complement each other, and actively exert the positive external effects of high-quality economic development. Environmental governance should not only involve the implementation of accurate pollution control according to the actual situation of the region, but also avoid regional fragmentation. Relying on the technology spillover effect of two-way FDI synergy, we should enhance our ability of independent innovation, accelerate the penetration of technology innovation into the ecological field, and take the road of sustainable green development. [ABSTRACT FROM AUTHOR]