The experiments of thermal shock damage on piston were conducted by shaped high power laser. Damage mechanism of thermal shock specimen was characterized by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The mechanical properties of thermal shock specimen were evaluated by microhardness. The corresponding mechanisms were discussed in detail. The results show that cracks originated from the interface of Al-matrix and intermetallic phase due to the thermal and mechanical misfit between these brittle components of the microstructure and the surrounding ductile matrix. Oxides of thermal shock crack can accelerate the damage of piston. There is a drop in the hardness of piston at all locations after thermal shock tests.