Electron beam welding process of AZ61 with 10mm thickness magnesium alloys was investigated. The influence of processing parameters including focusing current, welding beam current and welding speed was researched. The results show that an ideal weld bead can be formed by choosing processing parameters properly. Focusing current is main parameter that determines cross section shape. The beam current and welding speed are main parameters that determine the weld width and dimensions. The test results for typical welds indicate that the microhardness of the weld zone is better than that of the base meta1. A fine-grained weld region has been observed and no obvious heat-affected zone is found. The fusion zone mainly consists of small α-Mg phase and β-Mg17A112. The small grains and β phases in the joint are believed to play an important role in the increase of the strength of weld for AZ61 magnesium alloys.