In order to obtain wide-band and high-resolution monochromatic light, the wavelength of the imaging spectrometer was calibrated, and a scanning monochromator was designed. The grating scanning system was driven by worm and worm wheel mechanism, and an off-axis installation method was designed to install the worm gear, thus solving the problem of the traditional installation method, such as the decrease of the effective aperture of the grating, and the increase of the stray light. The monochromator optics system used the horizontal Czerny-Turner structure. It used three gratings to achieve 280-2 240 nm wide band output, which achieved the high diffraction efficiency and guaranteed the spectral resolution in the whole wavelength range. The output wavelength and the motor step number was non-linear in the process of worm gear scanning, so the monochromator system was calibrated by different mathematical models. The final experiment and the measurement proved that the spectral resolution of the monochromator was better than 0.1, 0.2, 0.4 nm at 280-560 nm, 560-1 120 nm, 1 120-2 240 nm respectively. Simultaneously the wavelength repeatability reached to 0.094, 0.186, 0.372 nm, and the precision reached to 0.096, 0.191, 0.382 nm. The monochromator achieves the design goals, and meets the requirements of the wavelength calibration of the imaging spectrometer.