The stirring effect of a rotating laser on a molten pool can expand the range of the laser heat source and effectively inhibit defects such as pores and improve the quality of the weld joint. Due to laser rotation, the physical characteristics of the heat source and the dynamic behavior of the keyhole and molten pool are more complicated than those of conventional laser welding. This paper adopts a numerical simulation method. A three-dimensional model is developed, which takes into account the coupling of the keyhole, recoil pressure and molten pool. The model can describe the dynamic behavior characteristics of keyholes and fluid flow and the formation process and mechanism of keyhole-induced pores in welds during rotating laser welding. It can be concluded that in conventional laser welding, the keyhole is deep, narrow and unstable, which usually results in the formation of bubbles. If the bubbles in the molten pool fail to overflow in time, pores are formed. With an increase in laser rotation frequency, the keyhole becomes shallow and wide, and the dynamic behavior of the keyhole tends to be stable, which can effectively inhibit the formation of pores. When the rotating frequency is increased up to 150 Hz, the formation of pores can be completely suppressed.