Abstract: The thermal noise sources from the accelerometer’ s sensor unit,such as radiometer eff ect,radiation pressure and residual gas damping were investigated.Their effect on the accelero meter’ s resolution was analyzed.Two methods were presented to reduce the thermal nois es.One is to stabilize the temperatu re around the sensor unit,the other is to lower the inner gas pressure.To meet the resolution of 1×10^-9 m·s^-2/√Hz within the bandwidth from 10^-4 Hz to 10^-1 Hz,the temperature noise must be controlled to lower than 0.25 K/√Hz if the gas pressure inside the sensor is 5×10^-4 Pa.