To space truss structure, a two-stage damage identification method was proposed. First, using the modal force vector difference with small and low order modes to identify the damage bar of the space truss structure, then identifing the extent of damage through the analysis method of eigenvalue sensitivity by use of the modal frequency with easy-get and high accuracy characteristics. Numerical analysis show that this method can effectively identify different types, different quantity as well as varying degrees of injury bar. the algorithm of the method is simple, small computational workload , and is apply to actually truss structure damage identification.