Abstract: Microstructures and properties of 20Cr steel and level-B steel joints welded by gas metal arc welding with ER50-6 wire are investigated with low-temperature impact,room-temperature tensile test,hardness test and metallographic analysis. The results show that the joints welded by gas metal arc welding with ER50-6 wire have better performance and more strength than parent metal. The microstructure of welded metal mainly contains reticular proeutectoid ferrite and a little carbon-free bainite. Carbon-free bainite also appears in the HAZ of 20Cr steel together with little lath martensite ,while in the HAZ of level-B steel ,little granular bainite distributes on the blocky ferrite.