A three grating monochromator with a wavelength range of 185~900nm was designed to meet the accuracy requirements of UV visible spectrum calibration; To improve the wavelength scanning accuracy of monochromators and reduce the engineering cost of high-precision wavelength scanning mechanisms. A model was established to investigate the impact of grating angle error on the wavelength accuracy of the scanning mechanism. A high-precision encoder based angle error compensation device was designed, and the accuracy correction of the wavelength scanning mechanism was achieved through compensation algorithms designed with different software parameter settings and algorithms; The experimental results show that after compensation through parameter algorithms, the wavelength accuracy and wavelength repeatability accuracy of the scanning mechanism have been improved within the working wavelength range. The degree of accuracy improvement varies under different wavelengths, with an improvement ratio of 20.8% to 35.2% for wavelength accuracy and 61.5% to 95.2% for wavelength repeatability accuracy. The above experimental results verify the effectiveness of the error compensation device and compensation algorithm, improve the accuracy of the wavelength scanning mechanism, and reduce the cost of high-precision wavelength scanning mechanisms in engineering applications.