Abstract: The vacuum vessel is the core component of the China future fusion engineering test reactor. Port stub is a part of vacuum vessel and it is welded by electron beam welding (EBW), which has capability to weld more than 50 mm thickness stainless steel by a single pass. In order to explore non-uniform properties of EB welded joint, beam oscillation was applied during the welding process and the microstructure and microhardness of 50 mm 316L austenitic stainless steel welded joint were analyzed. The results showed that the weld microstructure was composed of austenite and ferrite. From the upper layer near the center line of the weld to the lower layer, the microstructure changed from coarse lathy/skeletal ferrite to more close-packed skeletal ferrite and equiaxed gain. Welded joints with beam oscillation appeared equiaxed gain earlier in the weld thickness direction. Beam oscillation can improve the quality of the welds surface forming. The microhardness of the welds gradually increased from the upper layer to the lower layer.