Variable-capacitance micromechanical accelerometer is widely used because of its high sensitivity and low power. Therefore, the further study on its performance has much theoretical and applicable significance. This paper takes the closed-loop bias stationary comb-finger variable-capacitance accelerometer as an example, introduces its operation principle, establishes its mechanics model through analysis, and gives force balance equations. Then it researches and analyzes its performances such as electrostatic forces, full scale, stability, resolution and so on. Based on the model of the parameters from the accelerometer, key expressions were acquired. These expressions reflect and affect electrostatic forces, measure range, stability, sensitivity of the accelerometer. The results prove that performance of the accelerometer are connected with the dimension of the beam, the mass, the area of the pole plate, bias voltage, feedback voltage and so on. This work will provide a reliable theoretic foundation for the further optimum design of variable-capacitance micromechanical accelerometer.