The invention discloses a storage system online data compression method, device and equipment, and the method comprises the steps: carrying out the data compression after receiving a compression instruction, and obtaining a compressed data block; Searching corresponding segment metadata according to the main metadata, determining the initial position of the current blank storage area according tothe segment metadata, and storing the compressed data block into a physical disk according to the initial position; After a reading instruction is received, searching corresponding segment metadata according to the main metadata and the reading position of the reading instruction; Determining the position of the data to be read in the physical disk according to the searched segment metadata, and then reading the data; Wherein the segment metadata comprises feature information of segments, and the segments are storage area segments obtained by dividing virtual storage addresses corresponding tothe physical disks according to a fixed length; Wherein the main metadata comprises feature information of the segment metadata. The metadata is segmented, each segment corresponds to the virtual storage address with the fixed length, reading and writing of the compressed data are facilitated, the compression performance is improved, and management of the compressed data is facilitated.