Abstract: Based on the dynamic frame of CM1 model, it is found that advection, convection, grid spacing, humidity gradient, unstable stratification, water vapor content, temperature and sedimentation have a direct impact on the simulation of severe convection weather by equation deduction. While grid spacing, humidity gradient and unstable stratification are mainly reflected in the turbulent flow, the temperature effect is mainly reflected in the water vapor phase transition. An ideal simulation was performed using the sounding data that could stimulate the squall line process. Through scale analysis of model data, we found that advection, convection and the hydrometeor precipitation have the greatest influence on the change of moisture variables in squall line system, while the influence of water vapor phase change is the second, and the turbulence effect is relatively small. Therefore, the formation of squall lines needs the cooperation of water vapor distribution and the ascending air flow. Through the analysis of horizontal wind field and the change of water vapor disturbance, the effect of advection on water vapor transmission is verified.