Abstract: For the problems of low accuracy and difficult measurement in roll angle measurement,a roll angle measuring method based on spot position changes of collimated beams was presented. The positions of the two light spots on the CCD change with the movement of measured object, so does the slope of the line determined by the two light spots. The change of the slope is caused by yawing, pitching and rolling movements. In the measuring system, the pitch angle and yaw angle were measured based on the principle of self-collimation. After the affection of the pitch and yaw were eliminated, the roll angle was accurately measured. A mathematical model of the system was built,and Zemax software was used to establish a system model to simulate roll angle. Simulation results were calculated by the solving model of roll angle. Within the range of 0~1 800 the results of the mathematical model were exactly consistent with the value of Zemax, so that the feasibility and correctness of measuring method were validated.