Abstract: The gas damp of the two translational moving parallel flats in Micro Electro-Mechanical System (MEMS) devices is analyzed. The analytical formulae of the gas damp force and damp coefficient of the parallel flats in the MEMS devices are derived by expanding the vertical motion equations of the flat in Fourier series. The result shows that the gas damp coefficient of the translational moving parallel flats is close to be inversely proportional to the third power of the gas film thickness. The gas damp in a micro acceleration switch is simulated. The results show that the gas damp changes according to the switch working state. The effect of the gas damp coefficient upon the switch performance is also studied.