A study of equivalent circuit model of MQW lasers derived from three-level rate equations is carried out. It can explain the carrier distribution, which can not be explained by traditional two-level model. The simulation of modulation behavior is implemented in SPICE. Results of various modulation properties from the simulator are discussed. Especially, the scheme was implemented in a hierarchic way, which provides a much easier management and a help to realize photonic design automation (PDA).