Abstract: Using molecular dynamics methods combined with two-step radiation heating model, a complete microscopic description of the dynamic progresses involved in laser induced back-surface spallation in metallic film in stress confinement regime is provided. Different from the front-surface ejection with strongly affected mechanical stability of the front-surface by laser heating, the back-surface spallation is a disintegration of cold material. The mechanism of spallation is analyzed as a result of the interaction of the unloading wave and reflected stress wave. The propagation of laser-induced stress wave is also further investigated, and the influences of film thickness on spall thickness as well as the time when spallation begins are predicted.