The invention relates to a modified SHA-1 hash algorithm. The existing SHA-1 harsh algorithm has low security. The invention firstly adds a 1, a plurality of 0 and a 64-bit binary string after the information to be processed, then enlarges and groups the information, so the original 512-bit group is changed into a 1024-bit group and a register value is initialized; then a main cycle is utilized to sequentially process each group, the main cycle totally has four operations, and each operation contains logical function and compression function processing; and finally, after the processing of all the groups is completed, 160-bit message digest is output, and when the message digest is transferred, the message to be transferred is added with a safety hashed value. Through the algorithm of the invention, the original SHA-1 algorithm has more safety on message processing, and through modifying the logical function expression and the compression function logical structure of the algorithm, the efficiency of the SHA-1 algorithm is improved.