Abstract: Welding quality is an important factor affecting the performance and life of welded products.In order to ensure the quality of laser welding,it is necessary to monitor the state of penetration in the welding process,and then adjust the welding parameters to avoid defects.In this paper,laser fillet welding is carried out for 316L stainless steel.The weld formation with different melt states is obtained by changing the welding parameters,Xiris molten pool camera is used to obtain the image above the molten pool during the welding process,to observe the change of the molten pool and the plasma region under different melt states.The results show that when the weld is completely fused,the brightness of the plasma region observed by the melt pool camera varies drastically,and the fluctuation of the grayscale value obtained after image processing is large,while the opposite result is obtained when the weld is not fused.According to the results of feature extraction,9 groups of specimens were predicted,and it was concluded that the accuracy of melting penetration judgment under the prediction method reached 88％,which provided the implementation basis and theoretical basis for laser welding in the study of melting penetration,and had a wide range of application value in the actual production,and at the same time,it also provided reference and reference for the same industry,and promoted the development of laser welding technology.