Abstract: Using the low-order spectral model derived from the equatorial balanced model which includes cumulus heating,the solar radiation heating and the longwave radiation cooling two equilibrium states,are obtained.The mechanism for the active and broken phases of the monsoon in Southern Asia is illustrated.When the cumulus heating intensifies and the solar radiation heating decreases,the monsoon is active;the monsoon is broken while the cumulus heating decreases and the solar heating intensifies.