To address issues in security & the threat posed to the DES algorithm by brute force cracking, as well as the low efficiency of the 3DES algorithm, I propose extending the length of the DES algorithm’s key. First, change the block length of the DES algorithm from 64 bits to 128 bits and expand the key length of the DES algorithm to double length; secondly, iterative encryption is performed according to the new plaintext grouping and the expanded key length. The two groups are iteratively encrypted, and after every single iteration the two sets of R part data obtained from this round of encryption are exchanged, and then the next round of iteration; finally, the improved DES algorithm is compared with the DES algorithm and the 3DES algorithm by experiment. The results showing that the operating efficiency of the improved DES algorithm is better than 3DES algorithm. Therefore, the improved algorithm is proposed here greatly improves the security of the algorithm under the premise of ensuring operating efficiency and has good application value.