The transient thermal characteristics of InA1As/InGaAs/InP mid-infrared quantum cascade lasers in pulse driving conditions have been simulated by using the finite-element method, and evaluated experimentally. The results show that specific heat of the materials and heat capacity of the device should be take into account to simulate the thermal performance of the devices in pulse driving conditions. In this case, good coincidence of the simulation with the measured results has been reached and the much higher apparent thermal resistance of the quantum cascade lasers under pulse driving conditions could be explained.