The precast members for the large-span wall panels in the power distribution unit of substation are of large size. When the load distribution between the wall panel and the precast members is nonuniform and concentrated in some local areas, the stress in the local area will exceed the designed load. The stress concentration will result in the insufficient bearing capacity of the local precast member, and furthermore influence the whole performance of the wall panel and the practical application. In this paper, the key technology of digital manufacturing of large span wall panel precast parts in power distribution device building is proposed. The size data, shape data, material property data and connection mode data required by the wall are collected, then the wall model is established through the definition of the structure parameters using different commands in the BIM software. The correlation degree between the wall panel parameters and the precast member parameters is calculated, and the optimal mapping relationship of the structural parameters considering the strength of local member under concentrated load is obtained. Through virtual assembly of precast parts, combined with intelligent means such as collision detection, the digital production mode of precast member of the wall panel is constructed. The simulation test results show that the precast member model of the wall panel built by the proposed method fits well with the actual wall panel, with fit degree larger than 0.92, and the proposed method has better application effect.