A new analog mismatch model in circuit level has been developed. MOS transistor's small signal parameters are modeled in term of their matching character for both strong- and weak-inversion operations. Mismatch analysis on basic CMOS amplifiers are conducted with proposed model and Monte Carlo SPICE simulations. We successfully derived simple analytical formula on performance mismatch for analog CMOS circuits, which is verified to be accurate in using actual analog circuit design, within an average error of less than 10%.