Abstract: In order to solve the problem that the distance between laser port and calibration object couldn't be measured directly and accurately, a new method based on distance difference of calibration was presented. The moving distance of calibration object was used as the calibration input to improve the traditional calibration method of measurement system. Gaussian-Newton iterative method was used to calculate the parameters of measurement system. The extraction error and non-vertical error of laser image point were analyzed. The results show that the precision can reach 4.000mm. The method can be used to calibrate the distance between calibration object and laser port accurately.