An improved electrical equivalent circuit for a capacitive MEMS accelerometer, incorporating temperature, pressure and squeezed film effects is reported. The circuit model corresponds to a single degree of freedom (SDOF) vibrating system, including dominant micro physical mechanisms. Static, transient and frequency response analysis are carried out at temperature and pressure ranges of 100 K to 400 K and 30 to 3000 Pa respectively. The effect of these parameters on the resonance frequency, peak displacement and settling time of the accelerometer are determined. Simulations are performed using PSpice' circuit simulator.