In order to compare the performances of STAP for the underwater LFM with CW signal, the method of STAP for LFM was proposed. First, the principle of STAP for CW was analyzed, according to the underwater echo of CW. Second, the space-time steering vector of LFM is deduced by analysing the underwater echo of LFM. At last, the performances of STAP for LFM and CW were compared by simulation. The results show that the proposed method of STAP for LFM can achieve the good performance in target detection and tetection, but CW has the superiority in the performance of STAP.