This paper describes a method for building hot snapshot copy based on windows-file system (HSCF). The architecture and running mechanism of HSCF are discussed after giving a comparison with other on-line backup technology. HSCF, based on a file system filter driver, protects computer data and ensures their integrity and consistency with following three steps:access to open files, synchronization and copy-on-write. Its strategies for improving system performance are analyzed including priority setting, incremental snapshot and load balance. HSCF is a new kind of snapshot technology to solve the data integrity and consistency problem in online backup, which is different from other storage-level snapshot and Open File Solution.