In order to improve the measuring accuracy of roundness error of rotational parts,according to wavelet transform filtering algorithm and the least squares model,a roundness error detection system based on scanning laser differential technology were proposed.Two light beams with intensity modulation signals were formed by a spectroscope,and the influence of eccentricity error is eliminated in principle.The measurement of the roundness error was carried out for a calibrated part,and different experimental conditions were set.When the eccentricities are 2~4 mm,5~6 mm and 7~8 mm respectively,the difference of the roundness errors is less than 0.62 μm.The results show that the measurement system can effectively eliminate the eccentricity error and complete the roundness error detection of the rotational parts,which provides a new method for the high-precision measurement.