It is discussed in this paper the building up process of an integrated diagnosis system for satellites, which is based on the Multi-Signal Model method. The basic idea is as follows. Firstly, the Multi-signal flow graph model of the satellite is constructed, which can describe the testability character of the satellite clearly. Secondly, based on the model, a real-time fault reasoner is developed, which can detect the faults and indicate the suspected components of the satellite based on online telemetry data. Thirdly, the suspected components can further be isolated by activating an interactive fault diagnosis process. In interactive diagnosis, the diagnostic strategy is also acquired from multi-signal model and is expressed in the form of Bayesian networks to achieve self-learning ability. At last, an integrated diagnosis software platform for a satellite attitude control system with both real-time diagnosis and remote interactive diagnosis abilities is developed, and its performance is verified by simulation and actual test data.