Abstract: Based on semi-geostrophic PBL model and large-scale model, a diagnostic model to calculate boundary layer wind is introduced. The horizontal inhomogeneities of terrain and the roughness of ground, the temporal and spatial variations of large-scale pressure field are included in this model. A terrain coordinate transformation is introduced to compute the horizontal gradient of the geostrophic winds. The tower layer wind model is used to diagnose the boundary layer wind instead of the semi-geostrophic model for the lower latitude. The comparison with the observational data shows that the diagnosis has attained a fairly high level accuracy for both wind direction and wind speed. Therefore, it can be used in practice to diagnose or forecast the PBL wind when largescale model is incorporated.