In this paper, a northern-ward neutercance (8509) in its developing process was analysed using the full ω-equation. The result was compared with another typhoon (8406) whose early path and intensity were similar with 8509. The results show. (1) In the stage of tropical cyclone, the cumulus convective heating and large-scale latent heating are the main factors to maintain its vertical motion. (2) Temperature advection is the main cause and prior-condition to the reutercance. (3) cumulus convective heating also makes its important contribution to the reuter-cence, and has evident suppliment and strengthening effectness to the precipitation of typhoon rain area.