Abstract: The simulation of the monsoon circulation over East Asia was carried out by using a primitive equation model which includes various diabatic heating effects, frictional dispersion and moist processes with mountain. The results obtained coincide with the observations and show the existence of the two bands of precipitation.The several contrast experiments have been examined through decreasing moisture contrent in the atmosphere, eliminating cumulus convection and mountain effects .respectively. It is found that both the meridional monsoon circulation cells over 120°E and 100°E are very sensitive to the moisture fields.but the former is more sensitive than latter.The existence(nonexistence) of convectivecumulus process exhibits a significant effect on the enhancement (weakening)of the monsoon cells. The mountain shows stronger effects on the circulation over 100°E than over 120°E, which means that the causes of forming monsoon circulation are quite different between the two longitudes.