In order to study 1064 nm laser etching mechanism for aluminum thin films on polyimide substrate, the etching process of aluminum thin films is simulated by finite element analysis software ANSYS. By analyzing the laser energy absorbing and transforming process within aluminum thin films, temperature field distribution of thin films induced by laser ablation is obtained, and the separation mechanism of aluminum thin films from polyimide substrate resulted by the decomposability of polyimide is verified.