The design of symmetric cryptographic algorithms is composed of structure and internal permutation, but it is not a simple accumulation, the coordination and interaction between the structure and the internal permutation is also crucial, the corresponding cryptanalysis can help to the security evaluation and the design of symmetric cryptographic algorithms. Simpira is a family of cryptographic permutation. The overall structure is a generalized Feistel structure, and its F function is based on AES. The object of this paper is a structure mentioned in the Simpira document, which is a simplified case of Simpira-2. The algorithm's state size is 256 bits, and the overall structure is Feistel structure, whose F function is 1-round AES. This paper focuses on the simplified case mentioned above, so the 4-round truncated differential trail with 6 active S-boxes and the 5-round truncated differential trail with 15 active S-boxes are presented. By the computation and analysis of differentials in S-box and MixColumns, corresponding to the 4-round and 5-round truncated differential trails, the probabilities of two differential trails can reach 2^-36, 2^-91, respectively.