Abstract: The present invention discloses a computer-implemented method for compressing bi-level image files, during the computer-implemented process, said bi-level image files are to be compressed with the algorithm comprising following steps: abstracting symbols from the bi-level image files and re-sorting the symbols, and symbol encoding. The present compression method is based on symbols instead of pixels, the compression ratio of this algorithm is improved by 50% compared to the PDG format by BJSDCX, and is improved by more than 30%, compared to the NLC format by National Library. It is suitable for compression and management for archive files.