The melt pool, formed by the superheated molten metal, is the initiation of solid part and the general process of laser additive manufacture process. The transient phenomena in the melt pool are of paramount interest in obtaining an optimum mechanical performance. In this paper, the different transient evolution phenomena of melt pool for the moving and fixed laser beam during the laser irradiation process are investigated, then the quantitative competition effects of the laser parameters on those transient phenomena are also studied. The results show that the evolution of melt pool gradually enters into the quasi-steady-state for the moving laser condition, the deformation of free surface almost has no change near the forward of laser beam. However, the fixed laser condition has different evolution process and the deformation of free surface becomes larger and larger even piercing the workpiece. The melt pool evolution becomes vigorous and prone to enter the quasi-steady-state with the increasing energy input per unit area which directly dominated by the laser parameters. Further investigation on the quantitative percentage of each parameter on the evolution shows that the laser scan speed is the most important factor for the evolution of melt pool.