Abstract: The settling speed of switched-capacitor (SC) Amplifier is affected by the resistances of MOS switches. The closed loop transfer function of SC Amplifier with switch resistances is deduced using one-pole linear model of OTA. By analyzing the positions of poles and zeroes, the effects of switch resistances in two positions on step response are researched. An optimization method of MOS switches in practical design is proposed to decrease the settling time of SC Amplifier' step response. This method is verified by the simulation results.