To build an actual cloud energy storage system by blockchain for the ancillary service, this paper presents a prospective engineering planning method and design process to build a platform with five functions of cloud energy storage system. To demonstrate the feasibility, the engineering planning method includes the following steps. First, the detail design drawings of planning and feasibility analysis are introduced. The feasibility analysis including the project’s necessity, project alternatives, project impact, design drawings, construction scale are needed. Then, the device hardware design of blockchain platform with five functions is presented. Thirdly, the main material and equipment list, and the total investment are given. Finally, the post project evaluation is introduced. The functions include the peak load regulation, unit primary frequency regulation and automatic generation control, black start, reactive power and voltage regulation, reserve ancillary service for the integrated energy system. The paper can be referenced for planner.