A membrane rainwater treatment device comprises a rainwater well, an initial rainwater discarding device, a rainwater collecting pool and a treatment pool which are connected through pipelines in sequence. The upper end of the treatment pool is opened, a treatment pool body is divided into four pool bodies, namely, an anoxic pool body, an MBR membrane rainwater treatment pool body, a sludge pool body and a clean water pool body, through partition plates, two sewage lift pumps are arranged at the bottom end of the rainwater collecting pool, each sewage lift pump extends into the bottom end of the anoxic pool through a suction pipe, a submersible mixer is arranged at the portion, near the bottom end, of the anoxic pool, at least three flat membrane filter assemblies are arranged in the MBR membrane rainwater treatment pool, an air inlet formed in the bottom end of each flat membrane filter assembly is connected with a roots blower through an air inlet pipeline, an aerator pipeline is additionally arranged at the bottom of the MBR membrane rainwater treatment pool to be connected with the air inlet pipeline, a water outlet formed in the top end of each flat membrane filter assembly is connected with the clean water pool through a water outlet pipeline, two suction pumps are arranged in parallel on the water outlet pipeline, a drainage pipeline is arranged at the bottom end of the clean water pool, a suction pump is arranged on the drainage pipeline, and a disinfection pipeline is arranged on the portion, near the top end, of the clean water pool.