Abstract: Based on the conditional instability of the second kind (CISK), a dynamical study on the role of the tropical upper tropospheric trough (TUTT) for the generation of typhoon has been carried out. The results show that TUTT plays a certain role in the generation of typhoon, but this effect is very weak in comparison with Ekman pumping and the cumulus momentum transport. Therefore, for the generation and development of typhoon, the circulation pattern of the middle- and lower –troposphere in tropics should be paid more attentions too.