The invention relates to a wavefront sensor based on a circular transmission area modified Hartmann mask and a detection method. The wavefront sensor comprises a diffraction element and a detector, wherein the diffraction element is a hybrid grating formed by a checkerboard phase grating and an amplitude grating with a circular transmission area. The modified Hartmann mask has a better diffractionspectrum characteristic, namely, higher +/-1-level diffraction efficiency, than a modified Hartmann mask (MHM) widely used at present when being applied to four-wavefront shearing interference, thereby further reducing system errors in differential wavefront extraction process, and improving the measurement accuracy; and the wavefront sensor simplifies the grating structure under the premise of ensuring the diffraction efficiency through properly selecting a quantification factor of the amplitude grating, and the processing difficulty of the components can be reduced. The wavefront sensor canbe applied to the field of high-precision wavefront detection.