As two important policy tools to promote technological innovation, the effectiveness of government subsidies and tax preferences has always been controversial. In order to improve their effectiveness on promoting technological innovation, empirical evidence based on the data of A-share listed companies from 2009 to 2019, finds that both policy tools have a positive and significant impact on technological innovation, and the promotion effect of tax preferences is more significant. Further research shows that the two are complementary in their impact on technological innovation, and the combination of them can achieve a policy effect of 1+1>2. The reason is that the combination of the two can effectively alleviate the corporate financing constraints and improve the allocation of corporate human capital. Heterogeneity analysis shows that such complementarity is more obvious in high-tech enterprises, enterprises in eastern and northeastern regions, private enterprises and small enterprises. The research of this paper can provide reference for relevant policy making.