Based on the phase linearity of a pulse train, a coherency identification algorism is proposed to deal with pulse signals. The algorism is able to improve the signal-to-noise ratio (SNR) of the signal through coherent accumulation. The relationship between the threshold and the performance of the algorism is discussed in the paper. A formula of minimum SNR needed is presented. Simulation results show high performance of the proposed algorithm. The proposed algorism can be applied to the identification of the pulse Doppler radar. It also can help the development of the digital radio frequency memory (DRFM).