In this paper, an approach using a defocused Shack-Hartmann sensor for quantitative phase imaging (QPI) is proposed. In this technology, the defocused Shack-Hartmann wavefront sensor is used to record the intensity distribution under the illumination of light with two different wavelengths, and the dual wavelength phase retrieval algorithm is used for phase retrieval. The digital light field through the phase object is obtained, and the imaging of pure phase objects is realized. Numerical simulation results show that the QPI method is simple and with high accuracy and fast convergence, which is a very promising QPI technology.