We all know and often use compression software, why the compression software cannot reduce the file size after compressing the compressed file, and even multiple compressions will make the file size larger. Through research on compression software and compression algorithms, we found that based on previous theories, data compression has a limit. This article provides a new theory, expounds a new mathematical method, and implements a new compression algorithm, which can compress files multiple times and accumulate the compression rate, for example, compressing a 1Gb file into 1Kb.