The invention discloses a coding beam-splitting phase measurement device and method, and the device just needs one light spot detector, one weak scattering sample in the known distribution, two-dimensional gratings with the equal diffraction-order light intensity distribution, and a corresponding fixing device. The cost of the device is far less than the cost of a conventional interferometer, and the device exerts low requirements for the stability of an environment. A to-be-measured light beam is split by the gratings, and then forms a plurality of separated diffraction spots on an imaging target surface through the weak scattering sample in the known distribution. An iteration algorithm is used for processing each diffraction spot, and the wavefront amplitude and phase of the to-be-measured light beam are restored. According to the invention, the plurality of different diffraction spots are obtained through the splitting effect of the gratings. Compared with a method employing one diffraction spot for iteration restoration, the method is higher in resolution in an iteration restoration process. Because only one diffraction spot needs to be recorded, the measurement process is simple and quick. The device and method can be used for the wavefront detection of pulse laser, and provide a solution for the wavefront measurement.