The proposed optimum phase defocus grating for wavefront curvature sensing features an equidistantly quantized two-phase-step and a phase step height of p. The optimum phase defocus grating suppresses the influence of zero-order diffraction. The high diffractive efficiencies of the ?1 diffraction orders are verified experimentally, showing average values of 38.08% and 40.36% respectively. The phase plate introduces the wavefront deformation, which are measured by wavefront curvature sensing and reconstructed via the Green’s Function algorithm. The reconstructed wavefront is compared with the measurement result of a Veeco interferometer. It is verified that the measurement of the self-designed curvature sensor is correct. The error percent of peak-valley value (PV) is 10%, and the error percent of root mean square (RMS) is 2%.