Abstract: A method of acquiring B2a signal of BDS-3 is developed for accelerating no-prior-information cold starting of rescue positioning devices.Digital down conversion is done through matched filter and single side band acquisition is adopted to deal with the multi-peak characteristics of B2a signal autocorrelation.The matched filter correlator combined with FFT(Fast Fourier Transform) transforms the 2D(code phase-doppler shift) search into a single dimension(frequency) parallel search to accelerate the search process.The effect of the length of the matched filter and the number of FFT points on acquisition performance is derived and the relation between processing losses and correlator length for different doppler shift is analyzed.The suggestion about choosing of the parameter is given.Experiments show that correlation peak is high enough to achieve signal acquisition even when s/n ratio goes down to-30 dB.The design can achieve faster acquisition with better sensitivity while requiring lower sampling rate and less hardware resource.