Abstract: This paper describes the experimental results of the transient fracture ef- fect of aluminium plate in tension and irradiated by 8kW CW CO₂, laser beam. The study shows that the macro physical fracture or micro -damage of the plate caused by transient temperature elevation may evolve into the macro crack source of structure fracture. The large deformation and failure of structure are mainly attributed to the transient thermal softening of material, the corresponding redistribution of macro loading and deformation in the structure. The larger pretension the aluminium plate bears, the less the incident laser energy for fracture of the structure will be.