In the laser drilling process, the interaction between laser and rock is a complicated three dimensional (3D) unsteady problem. The thermal conduction model is established according to energy conservation equations, and the stress distribution is obtained in accordance with thermal stress theory and generalized Hooke′ s law. Based on the 3D finite element models, the effects of fragmentation and vaporization of malmstone under five kinds of continuous Gaussian distribution lasers with a fixed 0.2 mm spot diameter are estimated. The simulation results are that the primary failure mode of malmstone is vaporization if a specified continuous laser is used to break a rock with a large ultimate strength, however, the primary failure mode of malmstone is fragmentation if a rock has a small ultimate strength.