A weak periodic pulse signal detection method based on coherent accumulation and least-mean-square（LMS）adaptive process with a large tap-input vector is proposed.The fact that a large amplitude will arise to the Estimation Error under the adaptive processing of a pulse signal with an appropriate large tap-input vector is pointed out,which can be used to detect weak pulse signal after a further processing.Together with the coherent accumulation,this method can be adopted to detect the weak periodic pulse signals,which is of great significance in the return signal detection of high-repetition laser active detection system.The results of the simulation suggest that the method has a nice performance.The influence of the waveforms of the pulse signal and the tap-input vector to the detection performance is also analyzed,which revealed the importance of the selection of the tap-input vector.