Abstract: The behavior of the laser welding of magnesium alloy with several activating fluxes was studied under the same experimental condition.The results show that the addition of oxide and chloride activating fluxes can increase weld penetration and D/W (depth/width)ratio in the condition of low power laser welding.The flux SiO₂ can make the penetration increased as much as 220%.It is proved that the activating flux can be used to increase weld penetration and decrease the cost of laser welding of magnesium alloy thin plate.It is found that the heat input has a large influence on the increment of the weld penetration.The main reason for the increment of laser absorptivity is that fluxes absorb more laser energy and transmit it to the specimen during the early period of laser action.