A comparative study of the interactions of the millisecond-nanosecond combined-pulse laser and millisecond pulse laser with aluminum alloy is presented. During the interaction between the laser and aluminum alloy, the coupling effect of the nanosecond pulse laser on the molten pool formed by the millisecond laser is analyzed. During the nanosecond laser irradiation in the combined approach, the expansion velocity of the plasma plume reaches 600 m/s, while the laser ablation depth increased by approximately 9 times. Based on experiments, the high-speed shadow imaging method, correlation of the temperature evolution characteristics, and ablation morphology are considered for a comprehensive analysis. The coupling effect between the millisecond-nanosecond combined-pulse laser and aluminum-alloy molten pool phase is explained.