A kind of the conditional instability of the second kind (CISK)--overstability convec-tion presented in the hurricane model is investigated in this paper. The structure of thisunstable mode and the basic conditions to excite it are also shown for discussion. In the tropical atmosphere, the cumulus convection could excite the CISK oscillatoryunstable mode through the CISK mechanism, and the cumulus friction (cumulus momentummixing) gives a fundamental effect to produce this overstability convection. Some meteorologists assumed that the waves in the lower stratosphere in the tropicalatmosphere may be caused by the forcing of the condensation heating. The present investi-gation shows from the dynamic angle that the CISK-overstability convection excited by thecumulus convection heating, especially by the cumulus momentum mixing, through the CISKmechanism is a fundamental factor to drive the waves in the equatorial stratosphere and theoscillatory phenomena in tropical atmosphere. A kind of the conditional instability of the second kind (CISK) - overstability convection presented in the hurricane model is investigated in this paper. The structure of this unstable mode and the basic conditions to excite it are also shown in. tropical atmosphere, the cumulus convection could excite the CISK oscillatoryunstable mode through the CISK mechanism, and the cumulus friction (cumulus momentummixing) gives a fundamental effect to produce this overstability convection. Some meteorologists assumed that the waves in the lower stratosphere in the tropicalatmosphere may be caused by the forcing of the condensation heating. The present investi-gation shows from the dynamic angle that the CISK-overstability convection excited by the cumulus convection heating, especially by the cumulus momentum mixing, through the CISK mechanism is a fundamental factor to drive the waves in the equatorial stratosphere and theoscillatory phenomena in tropical atmosphere.