With the continuous development of information technology and the increasing of collaborative work, the traditional collaborative design can no longer meet the needs of complex engineering projects in modern buildings. In order to fill the gap of collaborative platform under EPC mode, this paper proposes and implements a collaborative design platform based on one-cloud and three-terminal architecture, which aims to solve the problem of multi-user, cross-platform real-time collaborative design. This paper mainly designs and develops the architecture of one-cloud and three-terminal. Through the deployment of private cloud platform, it realizes the multi-terminal collaborative design in plug-in end, Web end and mobile end, significantly improves the design efficiency and collaboration ability, reduces the communication cost and error rate, provides strong support for the development of architectural design industry, and has wide application prospects and promotion value.