A large-signal spice model of QCL is described, which is based on a set of rate equations. This model can also perform both small- and large-signal simulations. The dynamic responses obtained by using Spice simulator are obviously different from those in the interband lasers. No resonance peak is presented in the modulation response and the 3-dB bandwidth would reach tens of GHz. The turn-on delay time is on the order of ps that accord with the carrier lifetime of QCL. In addition, the dependency of bias current on the dynamic response are investigated. Results indicates that the bias current has a significant effects on the QC laser.