An additive manufacturing system is provided. The system includes: a stage, a powder supplying device, an energy beam generating device and an atmosphere controlling module. The powder supplying device provides powder to the stage. The energy beam-generating device generates an energy beam and directs the energy beam to the stage. The atmosphere controlling module includes at least one pair of gas inlet-outlet devices coupled around the stage, and a dynamic gas flow controlling device connected with the gas inlet-outlet devices. The dynamic gas flow controlling device dynamically controls an angle between a flow direction of the gas and a moving direction of the energy beam. The angle is predetermined by a scanning strategy.