For the problem of 1553B bus system testability modeling which has the character of bidirectional information transmission, to put forward a method of testability modeling for 1553B bus system based on multi-signal flow graph. On the basis of analyzing the bus topology, information transmission mechanism and fault mode of 1553B bus, to construct the multi signal flow graph model of 1553B bus system by modeling of bi-redundancy bus structure, multi-dimension function attribute definition, multi-work mode and test item definition. Finally, by analyzing of an example, it proved the effectiveness of this 1553B multi-signal flow graph constructed in this paper.