The development of the spacecraft system-level Design-for-Test is introduced. The advantages of adopting bus-based method for testability design is shown. A framework for the system-level DFT is proposed using a hierarchical structure. The complexity of system testing is reduced by dividing the system into modules. The functions of individual modules are tested by inserting test functions. A testability model is built based on multi-signal flow. For complex product, a stepwise integration test design method is used. The attitude and control system is selected to show the advantages of bus-based DFT. Large flow and fast speed of bus communication are fully utilized to solve test problem. The proposed method have advantages of improving the test efficiency and test level, as well as reducing the test cost.