Through the analysis of the microstructure,hardness test and pulsating tensile fatigue test,study the microstructure and properties of the plug welding joint of Q310NQL2 and Q345NQR2 corrosion resistant steels. The results show that,when the ER50-G mild steel welding wire is used for plug welding process,the structure of plug weld nugget zone is pearlite,ferrite and Widmanstatten structure. In the heat affected zone the pearlite become larger because of overheating. The hardness of nugget zone is the highest in the whole joint,and the hardness of heat affected zone relatively decreased,but the softening phenomenon is not obvious. The fracture of pulsating tensile fatigue specimen is located at the root of the side nugget zone of thin plate. The brittle structure and stress concentration here are the main causes of fatigue fracture.