With increase of terrorist blast, it is becoming more important for buildings to resist the blast load than before. This paper focuses on analysis of loss influence on key members of frame structures subjected to blast loading. The performance of a 5 storey frame structure with damage was evaluated on the assumption that whose key columns and beams had been lost after blast. By comparing the deformation and the internal force of the original frame with the corresponding items of the incomplete one, the impact of the key columns or beams on the performances of the whole frame structure was discussed. Numerical results show that the loss of either the key columns or the key beams will endanger the whole structure. Especially, the deformation and the internal force of the members adjacent to the missing key column have obvious increases. Consequently, the loss of the key column exerts a more serious impact on the building than that of the key beam.