Abstract: Based on Chose work,a strong ITCZ that occurred in Aug.,1979 along 20°N from the Indian Subcontinent to the western pacific Ocean is diagnosed and analysed using FGGEⅢ_b data. The results show that:(l)the cumulus convection can be represented well by the computed cumulus mass flux. (2) Due to the cumulus convection,there is an apparent vorticity source to increase positive vorticity at high level and an apparent vorticity sink to reduce positive vorticity at low level.