Feistel structure is widely used in the design of block ciphers. With many Feistel-type ciphers being designed, it is likely for some of them to have some similarity which can be shown in their differential characteristics or linear characteristics. Noticing two Feistel-type ciphers, LBlock and TWINE, have the same number of impossible differential chains using U-method without considering the details of S-boxes. In this paper, we first introduce a graph model to describe the topological structures of block ciphers, and then we prove the equivalence of LBlock and TWINE in structure using this model. Moreover, we present a matrix model for analyzing the similarity of two Feistel-type block ciphers.