A combination of large mass,weak spring and nano-grating is the key for a nano-grating accelerometer to measure nano-G acceleration.A novel compact nano-grating accelerometer integrating a large mass with nano-grating is proposed.First,the numbers of diffraction orders are calculated.Then,structure parameters are optimized by finite element analysis to achieve a high sensitivity in an ideal vibration mode.Finally,we design the fabrication method to form such a compact nano-grating accelerometer and successfully fabricate the uniform and well- designed nano-gratings with a period of 847nm,crater of 451 nm by an FIB/SEM dual beam system. Based on the ANSYS simulation,a nano-grating accelerometer is predicted to work in the first modal and enables the accelerometer to have displacement sensitivity at 197 nm/G with a measurement range of ±1 G,corresponding to zeroth diffraction beam optical sensitivity 1％/mG.The nano-gratings fabricated are very close to those designed ones within experimental error to lay the foundation for the sequent fabrication.These results provide a theoretical basis for the design and fabrication of nano-grating accelerometers.