Aiming at the mixed position estimation problem of AIS mixed signals, this paper improves the traditional double-window detection algorithm.This improvement is implemented due to the significant difference in amplitude and frequency between the mixed-part and the unmixed-part of the mixed signals.In order to estimate the demarcation point between the overlapping segment and the non-overlapping segment,the method considers the ratio of the signal energy of the mixed signals reaching the window.The modified decision function makes the estimation accuracy better than traditional one.At last,the simulation is carr ied out base the novel method.The results show it can accurately estimate the overlappi ng start and end positions of the mixed signals comparing with the traditional double-window detection method.