In order to study the pulse laser etching process of metal thin films on polyimide substrate, a two-dimensional transient physical model of Gaussian distribution pulse laser irradiation in composite material is established with the finite element analysis software COMSOL Multiphysics. The temperature distribution of metal thin films is calculated under irradiation of pulse lasers with different powers by means of solving the thermal conduction equations. The influences of different laser parameters on etching process are discussed. Simulation results show that the ablation depth is mainly affected by the laser power density, and it decreases at first and then keeps constant with increase of metal film′s thickness. During the etching process, it is appropriate to choose laser parameters of higher power and shorter pulse width in order to well protect the substrate from damage. As copper film etching is much more difficult than aluminum film etching, higher laser power density should be selected for copper film etching. Results are instructive and helpful to understand the actual laser etching process.