The water vapor image before the vortex formation was analysed,and by the numerical simulation of the vortex using η model, water vapor effects on rain and synoptic system have been investigated.Results are as follows:(1)the Indian Ocean and Arabian Sea are important water vapor sources in the middle and upper troposphere for the forming of the vortex over the Plateau.(2)There are favourable conditions in height and temperature fields for the vortex forming over the Plateau if the water vapor increases in the middle and upper troposphere over the west of India and Arabian Sea. (3)The numerical forecasting will be improved,by changing water vapor condition in the middle and upper troposphere in the south of the Plateau and Arabian Sea based on water vapor image.