A novel and universal mathematical description of the phase-to-height mapping relationship under divergent illumination is presented, which meets the condition of the imaging system axes being not perpendicular to the reference plane and the link of system′s two pupils being not parallel to the reference plane. In the proposed method, the undetermined coefficients are separated from the coordinate system, which are independence to the coordinate system, so the amount of sampling points for calibration is reduced greatly, and only two calibration planes are required. The experiment has verified the feasibility and validity of the proposed method.