A novel circuit simulation methodology, incremental circuit SPICE analysis, is presented with the foundational circuit simulation algorithm. When a circuit in design is modified from one version to another, only the change in the circuit is simulated and analyzed. The approach is well applied into design process for circuit parametric modification and functionality verification. By reusing simulation result from successive version, the algorithm reduces the duplicated operations in simulation. The examples show the new approach increases simulation speed about 10 times over the traditional method.