Effect of energy ratio on weld formation and energy efficiency in the dual beam welding process was systematically studied. Molten pool behaviors under different energy ratios were observed in real time by the high speed video system. Influence mechanism of the energy ratio on dual beam laser welding characteristics was also revealed. Results show that the weld penetration depth increases and then decreases as the energy ratio increases, while the weld width shows the opposite variation tendency. The minimum penetration depth and maximum width are obtained at the energy ratio of 50/50. Energy efficiency is significantly different from each other with different energy ratios. The maximum energy efficiency is 32.7% at the energy ratio 20/80, while the minimum is 27.8% at the energy ratio 50/50. Molten pool size is also affected by the energy ratio. Molten pool length increases first and then decreases, and the molten pool width always decreases with the increase of energy ratio. The effect of energy ratio on dual beam laser welding characteristics is mainly attributed to the variation of keyhole and molten pool flow pattern in the welding process.