The invention discloses an optical system wavefront measurement device and method based on a circular carrier frequency phase demodulation method. The device comprises a laser, a beam expander, a spatial filter, an optical system to be measured, a point diffraction plate and a CCD camera, wherein the laser, the beam expander, the spatial filter, the optical system to be measured, the point diffraction plate and the CCD camera are sequentially coaxially arranged in the direction of an optical path; the spatial filter is arranged on the focus of the beam expander; the point diffraction plate is arranged on an emergent wave surface rendezvous point of the optical system to be measured; the point diffraction plate comprises a pin hole and a pin hole peripheral part, and the pin hole peripheral part is plated with a high-reflection film layer. The measurement method includes the steps that before an ideal wave surface generated by the point diffraction plate through the pin hole diffraction effect is used as a reference wave, the point diffraction plate moves in the direction of the optical axle to form a circular carrier frequency interferogram, and a four-phase splice method is utilized to directly solve original phases in the circular carrier frequency interferogram, namely the wavefront of the optical system to be measured. According to the method, the emergent wavefront of the optical system can be measured by few components, and the measurement device is easy to operate, high in accuracy and capable of meeting the requirement of transient measurement.