Weld bead profile is highly related to the dynamic behavior of keyhole and molten pool. In this paper, a three-dimensional transient model is developed to investigate the weld bead profile transformation considering the keyhole and molten pool dynamic behaviors in high power laser welding. In the model, multiphase including the solid phase, liquid metal phase, metal vapor phase and air phase is considered. A variety of physical factors are taken into accounts such as melting and solidification, evaporation and condensation, fluid flow, Marangoni shear stress, recoil pressure and surface tension. An adaptive hybrid heat source model is used to fit well with evolution of the keyhole. Volume of fluid (VOF) method is adopted to track the multiphase interface. The weld bead profiles can be classified into three types and the welding process parameters are closely related to the weld bead profile transformation. The simulation results show that the fluid flow, temperature field and mechanical equilibrium in the molten pool are the essential factors that affect the weld bead profile transformation. The relationship among the welding process parameters, mechanical equilibrium, fluid flow and weld bead profile transformation is analyzed. The proposed numerical model exhibits good agreements with the experimental results with respect to the weld geometry. (C) 2017 Elsevier Ltd. All rights reserved.