Abstract: In order to solve the problem of PB grade hardware demand in the mass storage system research process, a capacity simulation technology based on iSCSI protocol was proposed.Through the analysis of the file system format, a kind of more general mapping scheme and dynamic capacity mechanism were put forward further.At present, iSCSI provides a remote storage mechanism, on the basis of which we simulate disks using certain size files.The capacity are virtually enlarged and managed by address mapping, implementing the simulation from small files to large disks.At the same time, dynamic capacity expansion mechanism was introduced.At last, through experiments we test and analyze the performances between virtual disk and common disk, proving the feasibility and correctness of the technology.