Abstract: The dynamic mechanism of the maintenance of the monsoon circulation is investigated by the barotropic shallow water equation and with the aid of the low order truncated spectral model.The results indicate that the wave-wave non-linear interaction between the components of the geostrophic or ageostroph-is flow themselves,that between the geostrophic flow and geostrophic deviation as well as that between the geostrophic or ageostrophic flow and the geopotential field and the large scale external forcing are probably the determinan dynamic mechanisms of the maintenance of the monsoon circulation.