Abstract: Aimed at dealing with the acquisition of PN phase in direct-sequence spread-spectrum system (DSSS) system, by analyzing the construction of the modulated signal, a novel non-coherent approach to PN code acquisition technique for M-ary orthogonal signals in a DSSS system, based on non-coherent maximum-likelihood block estimator (N-MLBE), is proposed. The integrated maximum likelihood function is turned to two parts, which are realized with two matched filters. The proposed acquisition method is suitable to FPGA implementation. Combined with the multi-codes accumulation cell, the performance at low signal-to-noise ratios (SNR) is improved obviously. Its performance in M-ary MSK system, as well as its impact on factors such as frequency shift, signal noise ratio (SNR) have also been shown. Simulation results and analysis show that this algorithm is able to capture PN code at low SNR.