In order to improve the spectral absorptivity of infrared microbolometer, a metal grating absorption promoting structure based on surface plasmon was designed, and the influence of grating structure parameters on the spectral absorptivity was studied. Using the gold as grating material and the resonance structure of plasmon, the high reflectivity of metal material is overcome to enhance the infrared absorption capacity of infrared microbolometer. By changing the structure parameters of the grating and adjusting the resonance wavelength of the plasma, the spectral absorption efficiency in the working band of the infrared microbolometer can be improved. The influence mechanism of grating parameters on spectral absorptivity was analyzed by finite difference method. The regulation of the period, duty cycle, position and height of metal grating on spectral absorptivity was studied. With the grating period increasing from 2 to 5 microns, the peak wavelength of the absorption peak has a significant red shift, and the height of the absorption peak has a significant change. Although the overall trend is downward, the absorption peak at 3 microns is slightly higher than that at 2 microns. As the duty cycle of grating increases from 0.2 to 0.5, the infrared absorption peak shifts to short wavelength, and the height of the absorption peak increase gradually, but the width also narrows slightly. With the increase of grating thickness, the peak value of absorption peak is not affected very much, especially when uhe thickness increases to a certain extent, the peak value remains basically unchanged. however, the peak wavelength decreases with the increase of thickness. With the increase of thickness, the peak wavelength decreases slowly, and basically maintains near 10.6 μm. Based on the analysis of the mechanism of the influence of grating structure parameters on spectral absorptivity, the infrared absorption of vanadium oxide infrared microbolometer is greatly improved by further optimization of grating structure parameters. The average absorption of 8～14 μm is 61.6%, and the peak absorption is over 99%. The research on the absorption-promoting structure of metal grating has important guiding significance for the design of high-performance infrared microbolometer.