Based on a typhoon numerical model with horizontally threefold structure, a numerical model, in which the Qinghai-Xizang Plateau and its leeward side different scale orographic effects can been considered, is developed to study on a southwest vortex process during the period from 20:00 BST 12 to 20:00 BST 14 July, 1981. Comparison of the three numerical experiment results——with real orography, one third orography and without orography——shows:the features of the southwest vortex such as its movement, development, shape and domain, as well as the distribution and centres of its precipitation can be well simulated in the experiment with real orography.however, in other two experiments, it is failed to simulated out these features.Furthermore, the axis of the jet stream takes northward direction in the experiment with real orography, but it takes eastward either in the experiment with one third orography or in that without orography.Instead of appearing the shear-convergence flow pattern in the experiment with real orography, the wind field appears a deep trough pattern in that case without orography, so the massive northwest colder air mass moved southward.