Abstract: A two-dimensional numerical model has been developed to simulate the evolution of the nocturnal bou ndary-layer over a sloping terrain. The results are compared with the data observed in a mountain area north of Beijing. The depth and shape of the inversion layer and the profile of the downslope wind in this simulation agree with the observational ones. This model seems to provide a tool for solving the development of the nocturnal boundary-layer over acomplex terrain.