An integration circuit (IC) simulation method includes: (a) providing a design netlist of a system-level circuit, wherein the system-level circuit comprises a first sub-circuit; (b) providing a first behavior model that is determined based on an operation of the first sub-circuit, wherein the first behavior model is a function of one or more respective behavior-level parameters; (c) incorporating a first variation into each of the one or more behavior-level parameters of the first behavioral model; and (d) simulating the system-level circuit based on the one or more behavior-level parameters of the first behavior model that incorporates the first variation.