In this paper, the relationship between lowlevel jet(LLJ) and inversion layer over agroforestry system of Huang Huai Hai Plain are studied with a turbulence equation set. The results show that the luxurint farmland windbreak system vegetation can intensify the inversion intensity near surface effectively in late spring and early summer, and the existence of inversion may be beneficial to the formation of LLJ, the deeper the inversion is, the stronger the jet. The effects of external forcing such as geostrophic forcing and roughness on the formation of the jet are discussed with above equation set, too.