A limited-area numerical model is used to simulate the "73.7"rainstorm over the belt along the Yellow River from the Sanmen Gorgeto Huayuankou and the adjacent regions. Following Lavoie’s work(1972), a 3-layer atmospheric structure is presented which consists of:i) a constant-flux layer (in contact with the surface); ii) a well-mixedlayer (capped by an inversion) and iii) a deep stratum of stable air.For the well-mixed layer the average is obtained from the governing primitive equations and the other two layers are properly parameterized. The governing equations are solved numerically for mixed layer with consideration of the effect of its initial conditions on the follow-ing factors such as terrain influence, surface roughness, temperature variations, moisture fluxes and the release of latent heat. Results obtained by this model are close to those observed.