Aiming at the inner spline-bevel gear composite gears shaft’s coaxiality error measurement, this paper presents a non-contact optical measurement method based on a laser displacement sensor (LDS) and spectral confocal sensor. According to the least square circle (LSC) to calculate the center coordinates of the section, and the space least square fitting to get the reference axis. A standard part is used to calibrate the sensors’ installation errors, and use CMM to verify the system’s accuracy. Ten sets of measurements are made for the same internal spline-bevel gear part, in conclusion, the measurement uncertainty is 0.028 mm, the repeated measurement error is not more than 0.015 mm, the accuracy of the measurement system is 0.055 mm, can meet the needs of industrial production which required accuracy is 0.1mm.