A novel method for roll measurement is presented based on one-dimensional grating. The effects of straightness errors are avoided by using the measuring unit consisting of a focusing lens and photodetector. This method realizes errors separation, avoiding crosstalk of pitch angle and yaw angle, and enhances the ability of anti-interference by adopting double optical paths differential measurement based on the ±1 order diffractive beams. Feasibility of the method is analyzed in detail. Calibration curve, whose linear dependency is 1, is obtained by experiment. The results show that resolution of the rolling error is less than 0.6″. The method is simple and flexible enough to meet the different accuracy demands just by choosing the different gratings.