Abstract: The electron beam welding technology of 45CrNiMoVA steel was analyzed and discussed in the paper, and the microstructure, profile and mechanical properties of weld were examined by metallography, scanning electron microscope and fracture analysis, etc. Then, we analyzed the factors causing cracks and methods to prevent them, and chose the reasonable process weld depth being 20 mm. The results showed the weld of 45CrNiMoVA steel welded by electron beam had demonstrable superorities—good mechanical properties and high strength, well results were got by colored detecting on surface, and X-ray detecting carried on the weld.