Abstract: This paper deals with the microstructure and properties of electron beam welded joints of 30CrMnSiNi2A super high strength steel.The tests results show that the microstructure of the welding line under the as welded condition is typical coarse spiculate martensite and retained austenite; the microstructure of the welding line and HAZ is tempered martensite and retained austenite under 900℃ oil quenching and low temperature tempering.All of the fractures during the tensile tests of electron beam welded joints under as welded condition occurred in the base metal due to its comparatively low strength.Through the above mentioned heat treatment,the strength of the base metal increased distinctly,the welding line obtained favorable mechanic property with its elongation nearly doubled despite of a slight decrease in strength.The reason why the impact and fracture toughness of the welding line and HAZ are low after above mentioned heat treatment is a comparatively high carbon content in the martensite.Due to the small grained and even microstructure,the welding line showed comparatively high fracture toughness compared with the HAZ.