Abstract: Due to the global coverage of Beidou navigation satellite system, it shows the potential to be the opportunistic transmitter in passive radar marine detection. This paper focus on the passive multistatic radar constituted by multiple BeiDou satellites, and proposes a target echo space-time integration method to achieve maritime moving target detection and localization. First, this paper proposes a range reversal and azimuth stretching transform (RRAST), which converts each two-dimensional echo in fast-time and slow-time domain into a one-dimensional azimuth signal, and sets the Doppler centroid of each echo to zero. Then, the dechirp integration transform (DcIT) is applied to achieve the long-time integration of each echo. The incoherent summation of multistatic echoes is performed to accomplish spatial integration, achieving the maritime moving target detection in the Doppler frequency rate domain. Finally, the multistatic echoes are all projected to the target motion parameter domain, and the target localization and velocity estimation can be achieved according to the peak position. The simulation results show that the proposed method can realize the maritime moving target detection and localization under the condition of low signal-to-noise ratio.