Abstract: Combining EDA tools Cadence and a well established commercial simulation program based on finite element method ANSYS,this paper simulates the transient thermal effect of integrated circuit on layout-level. After obtaining electronic parameters especially power dissipation of the circuit,the transient temperature distribution is calculated by loading them into the thermal subsystem established by ANSYS. Based on a simple integrated circuit,we obtain the thermal time constant by adjusting the pulse-length,and simulate the thermal response under pulse with the same frequency and the same duty ratio but different duty ratio and different frequency.