Direct phase measuring deflectometry (DPMD) solves the measurement problem of discontinuous mirror objects. It uses a new mathematical model to directly establish the relationship between phase and depth. In the DPMD system, a liquid crystal display (LCD) is used to display a high-contrast fringe pattern, and a camera captures the deformed fringe image reflected by the mirror surface to be tested. However, the refractive effect of the LCD transparent layer causes errors in the DPMD measurement results. Therefore, we propose a method for compensating the refraction effect of the display in the DPMD system. By establishing a single layer refraction model, the thickness and refractive index of the transparent layer are first calibrated using the light equations, and then the refraction angle is calibrated using the system’s geometric relationship. Finally, the offset is calculated based on the calibrated parameters to compensate the system's depth data. The measurement results of a specular step and a concave mirror show that the measurement accuracy is enhanced by 30%. Therefore, this method effectively increases the measurement accuracy of the DPMD.