A low-g grating-type MEMS accelerometer comprises a glass base. One side of the glass base is connected with an LED light source, the other side of the glass plate is externally connected with a glasscover, an MEMS chip is packaged between the glass base and the glass cover, a spring mass system on the MEMS chip is suspended, and the glass cover is connected with a photoelectric detector; the spring mass system is integrated and includes a mass block fixing frame and a mass block, two sides of one end of the mass block are with the mass block fixing frame through springs, one side of the other end of the mass block is connected with the mass block fixing frame through a spring, and the mass block is supported and suspended through springs; the mass block is engraved with an indication grating, the glass cover is engraved with a scale grating, the two gratings are at a small angle, the LED light source is irradiated to the indication grating and the scale grating through the glass baseto generate moire fringes, and the spring mass system transfers an acceleration signal to the displacement change of the gratings, so that the acceleration is obtained by detecting the change of themoire fringes. The low-g grating-type MEMS accelerometer has the advantages of ultra-low g value detection and high sensitivity.