The invention discloses a phase retrieval based 4f mirror surface detection imaging system and a phase retrieval based 4f mirror surface detection imaging method. The system comprises a laser, a neutral density filter, a microobjective, a pinhole, a measured mirror surface, a 4f imaging unit and a computer, wherein the 4f imaging unit comprises a lens 1, a space light modulator, a lens 2 and a charge coupled device (CCD) camera. The light emitted by the laser irradiates the measured mirror surface after passing through the neutral density filter, the microobjective and the pinhole. The CCD camera arranged in the 4f imaging unit is used for acquiring a plurality of times of a light wave modulation image, and then the image is sent into the computer for sparse constraint phase recovery treatment. Based on the acquired light wave intensity image of the measured mirror surface, the method utilizes the sparse constraint phase recovery treatment to obtain the phase position of the light wave on the measured mirror surface, thus realizing the error detection for the measured mirror surface. The invention has the advantages of being high in accuracy, good in stability, simple in operation and good in noise robustness.