Abstract: Low-orbit satellite communication system has the features of low SNR receiver, large Doppler shift and fast capture requirement. To meet those demands in concealing communication, this article presents a time-frequency two-dimensional quasi-parallel multi-symbol cumulative capture algorithm. The critical parameters of the algorithm have been designed and optimized. The loaded prototype and signal processing platform have been built to test the performance of the designed algorithm. The test results show that all the indexes meet the project requirements. Under the conditions of that the symbol rate is 1 ksample/s, Doppler frequency shift is ±50 kHz and the receiver E_s/N₀ is no more than 3 dB, the capture time is less than 100 ms and the probability of missed detection is less than 0.003.