A modular storage system is provided for storing a disk array consisting of multiple hard disks. Each hard disk is provided with a terminal set. The modular storage system includes a casing having a plurality of disk compartments for receiving the hard disks respectively, a front end defining a front opening and a rear end defining a rear opening; a rear cover for covering the rear opening of the casing; and a plurality of connectors mounted on the rear cover via a coupling mechanism so that each of the connectors is aligned with a respective one of the disk compartments. Once the hard disks are installed respectively in the disk compartments, the terminal set of each of the hard disks is coupled electrically to a respective one of the connectors on the rear cover.