Abstract: Based on the characteristics of space truss structures, the concept of sensitive mode shape is introduced and an algorithm for its determination is presented. The damage location is determined based upon the residual modal force theory and with the assistance of sensitive mode shape. An evaluation algorithm based on the modal strain energy theory is given adopting an indeterministic equation group solved by the non-negative least-square method to quantitatively identify the damage extent. A practical space truss structure is used in the simulation to demonstrate the feasibility of the proposed algorithms on damage detection of space truss structures. Meanwhile the evaluation results on the damage extent are compared with those obtained by using the minimum rank perturbation theory with the consideration of measurement noise in the mode shape. The results show that the two methods are complementary to each other. They are both applicable to not only single damage but also double damages. The damage evaluation result is better and more reasonable than those obtained by only the minimum rank perturbation theory. It is feasible to be applied in fault diagnosis of space truss structures.