Abstract: An efficient method that can blindly estimate and synchronize to PN sequence of direct sequence spread spectrum (DS-SS) signal quickly is presented in a non-cooperative context. The method is based on the character of the DS-SS signal, firstly the period of PN sequence is estimated with a second-order cyclic-cumulant, and then the method of segmented cross-correlation is used to identify the synchronous start bit of the PN codes. The intercepted signal is divided into windows, from which the cross-correlation average is computed, and then the multiple correlations are utilized to estimate the PN sequence. Both theoretical analysis and simulations show that this method can get a good estimation without prior knowledge even if the intercepted signal is far below the noise, and it also has no hypothesis on the nature of the PN code sequence.