The invention provides an ultra-rapid X-ray diffraction imaging method and system based on a flash X-ray machine. The system comprises the flash X-ray machine which comprises a flash X-ray diode and further comprises a diffraction regulation subsystem, a detector subsystem and an auxiliary regulation subsystem. According to the method provided by the invention, a new diffraction light path regulation method is adopted, that is, a direct-current X-ray machine, a diffraction regulation system and a counting type detector are assembled, and after an accurate diffraction angle of anode characteristic line energy of the flash X-ray diode is determined, a plane-array detector is utilized. With the adoption of the method provided by the invention, the problem that a flash X-ray diffraction light path is difficult to regulate can be solved; and meanwhile, the signal-to-noise ratio of a diffraction image can be improved by a determined accurate diffraction angle and the complexity of the system is greatly lowered.