Based on the theory of endogenetic economic growth, we explored mechanism of technology spillover of FDI from three aspects including total factor productivity and effect of technology spillovers of FDI and absorptive capacity, and set up a basic model of technology spillover of FDI and a spillover model based on absorptive capacity, studied the series data of Changchun City in recent twelve years empircally. The results show that there is positive spillover effect of FDI in Changchun City which promote improvement in total factor productivity to a certain extent. There is nonlinear relationship of quadratic function between absorptive capacity and technology spillover, when absorptive capacity reaches a certain marginal value, the spillover effect of FDI will reach its maximum value.