Abstract: In this paper, a blind despreading algorithm is proposed for the synchronous multi-user long-code Direct Sequence Spread Spectrum (DS-SS) signals in low Signal to Noise Ratio (SNR) scenarios. The synchronous multi-user long-code DS-SS signals are represented as the short-code ones with missing data, and then the users spreading waveform subspace is estimated by the Singular Value Thresholding (SVT) algorithm. Finally, the Expectation Maximization (EM) algorithm is used to blindly despread the signals. The simulations show that the proposed algorithm has nearly performance with the cooperative dispreading in low-SNR scenarios.