Foreign direct investment (FDI) is an important external force for the upgrading of China's industrial structure. In this paper, the quality and quantity of FDI are parameterized, incorporated into the same theoretical framework, and the unbalanced growth model is established. The internal mechanism of the impact of the quality and quantity of FDI on the adjustment of industrial structure is analyzed. On this basis, a dynamic panel model is constructed to conduct an empirical test. The research shows that the improvement of FDI quality has a positive effect on the optimization and adjustment of industrial structure, and there is an internal mechanism for FDI quality to promote the improvement of regional technology level and further promote the upgrading of industrial structure. There is a nonlinear effect of the amount of FDI on the adjustment of industrial structure. Only when the amount of FDI reaches a certain level, can FDI’s amount increasing contribute to the optimization and adjustment of industrial structure. The internal mechanism is that the increase of the amount of FDI can improve the production and investment level of non-agricultural industries and promote the upgrading of industrial structure. At the same time, the pure increase in the amount of FDI will inhibit the improvement of the technical level of non-agricultural industries and hinder the optimization and adjustment of industrial structure. Only when the promoting effect of the increase in the amount of FDI on the investment level is greater than the inhibiting effect on the technical level, can the increase in the amount of FDI be manifested as the promotion for the adjustment of industrial structure.