Long-time integration technique is an effective way of improving target detection performance for unmanned aerial vehicle (UAV) in the passive bistatic radar (PBR) field, while range migration (RM) and Doppler frequency migration (DFM) may have a major effect on the integration capability as a result of target maneuverability. This letter proposed an innovative long-time coherent integration approach, regarded as Continuous Radon-matched filtering process (CRMFP), for low-observable UAV target in PBR. It not only mitigates the RM by collaborative research in range and velocity dimensions but also compensates the DFM and ensures the coherent integration through the matched filtering process (MFP). Real-life data following detailed analysis verify that the proposed method can overcome the Doppler mismatch influence and acquire comparable detection performance.