Abstract: The method of combined heat source is adopted to describe the welding energy distribution. The electron beam welding process of the digital array module shell is numerically simulated and is compared with experimental results. On this basis, four different lapping forms and the process parameters are optimized. The results show that the lapping form of 0.6 mm width four-side steps can obtain enough melting depth, and the distance from the root of the weldjoint to the edge of the step is small. The risk of subsequent corrosion can be avoided. It is a preferential structural form. The use of high heat input is beneficial to obtain wide weldjoint and to fill the gaps of the steps.