The diameter and roundness measurement of ring workpieces based on the laser displacement sensors is widely used in the measuring process of the product quality in the industrial site. The effect of angle setting errors of laser displacement sensors on the measurement of the workpiece’s diameter was studied, and the calibration method of them was proposed. Firstly, the relationship between angle setting errors of displacement sensors and calculated errors of the diameter was analyzed quantitatively. Secondly, a calibration method was proposed, which could calculate the angle setting errors of the sensors in accordance with the measurement data of three displacement sensors, and the diameter of the standard circle was unknown. The modeling process of the calibration method was illustrated and the effectiveness of the method through simulations was confirmed. Finally, the angle setting errors were calibrated by using coordinate measuring machine. The experiment result shows that the absolute errors of diameter are improved from 20 μm to 1.5 μm after calibration.