Abstract: In order to study the burning loss of magnesium element in laser welding aluminum alloy,a specially-designed device was first used to collect the spectral signals emitted from the keyhole plasma in deep penetration laser welding aluminum alloy 5052.Then,the content of magnesium element in the welds was tested by an electron probe micro analyzer.Under the experimental conditions,the welding parameters heavily affect the spectral intensity of magnesium element plasma.The spectral intensity is not uniformly distributed in the keyhole region.In the radial direction,the spectral intensity of MgⅠ decreases from the center to the edge of the keyhole;in the depth direction,from the top to the bottom of the keyhole,the spectral intensity of MgⅠ increases first and then decreases.The Mg content changes inversely with the spectral intensity in the keyhole region.Therefore,spectral analysis technology can be used to monitor the burning loss of magnesium element in laser welding aluminum.It can be concluded that Mg loss in the keyhole region is determined by laser intensity absorbed there.The higher the absorbed laser intensity,the bigger the Mg loss.