The design content of the secondary circuit of a substation cannot be obtained by computer using the CAD drawing expression method. Thus a complete digital design process of the secondary circuit is proposed, and the modeling scheme of secondary equipment and circuit for substation digital design is studied. Starting from the requirements of secondary circuit digital design, this paper analyzes the requirements of different departments for secondary circuit modeling, and focuses on the physical properties and connection properties of equipment. In the modeling scheme, the scope, object and language of intelligent modeling are defined, and the modeling of secondary equipment and digital design of secondary circuit are realized by modeling tools. The design effect of the pilot project verifies the feasibility of the scheme. This work is supported by the 2018 Annual Science and Technology Project of China Southern Power Grid (No. ZDKJXM20180001).