Abstract: After the operation of Chongqing-Hubei back-to-back flexible DC project in China, the main problem in the asynchronous operation of southwest power grid has become its own frequency problem, and the existing stability control system can only solve local problems, so it is necessary to construct AC/DC coordinated control system of southwest power grid. The design of AC/DC coordinated control system for southwest power grid is analyzed in terms of processing means, coordination modes and construction modes. The overall architecture of the system is described in detail, and the principles of construction are introduced in the aspects of site configuration and communication design. The function of AC/DC coordinated control system is described in detail from the aspects of fortification principle and control strategy of AC/DC coordinated control system. Moreover,the AC/DC coordinated control system is applied to the actual southwest power grid of China, and the detailed test verification is carried out at the same time.