Abstract: A non-dimensional secondary circulation equation for typhoons has been derived and then 11-yr compositing typhoon data were used to estimate the thermally forced secondary circulation. The main results have been obtained as follows:1.The diabatic heating and Cu vertical heat mixing are major thermal forcing factors. They have the same magnitude of order; 2.The effects of eddy flux and Cu horizontal mixing of heat are of minor importance; 3.Ekman pumping and Cu vertical heat mrxing cooperatively work. This feedback process is favorable for the enhancement of the secondary circulation of typyoons.