The invention provides a data deduplication method based on internet small computer system interface (iSCSI), belongs to the technical field of computer information storage, and is suitable for an iSCSI-protocol-based internet protocol (IP) network remote mirroring system. In the invention, bandwidth simplification and synchronous time reduction can be realized through deleting repeated data of an iSCSI write data block on the premise of not changing the structure of the conventional IP network remote mirroring system. The data deduplication comprises two stages: in the first stage, a coarse-grained similarity data chunk detection technology is adopted, and a content-defined chunking (CDC) algorithm and a bloom filter algorithm are combined to search similarity chunks in a full range, so that the data deduplication can be more flexible and more accurate; and in the second stage, an improved fine-grained similarity data chunk detection technology is adopted, and a fixed-sized partition and sliding window method is combined, so that the deduplication is performed on chunks rather than files, and transparency of deduplication to users is realized.