X-ray detectors have broad applications in medicine and industry. Although flexible lead-free perovskite films are competitive because of their lightweight and low toxicity, they are less efficient due to low charge transport. Herein, we report low-toxicity, flexible X-ray detectors based on p-type doped MA₃Bi₂I₉(MA=methylammonium) perovskite filled membranes (PFMs). Strong coordination between dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) and MA₃Bi₂I₉and the establishment of charge-transfer complex (CPX) improved the conductivity by four times. The flexible X-ray detector achieved a high sensitivity of 2065 μC Gy_air⁻¹cm⁻²and an ultra-low detection limit of 2.71 nGy_airs⁻¹, which is among the highest values in all environmentally friendly flexible X-ray detectors. Importantly, the PFMs retained excellent charge transport under mechanical stress. All of those make flexible MA₃Bi₂I₉membranes more competitive as next-generation X-ray detection.