A cache device comprises a hard disk, cache control unit and at least one flash memory, whereby the cache control unit controlling and regulating the flash memory as the hard disk cache device. The present invention method is defined by setting up a management table to manage each corresponding logical block address of the flash memory through a cache data read-out step and cache data write-in step in order to manage the cache read or write action of the flash memory on the hard disk. In addition, the step of recycling a cache space and replacing cache temporary data storage is to remove and replace temporary cache and storage space within the flash memory on the hard disk. Moreover, the step of reconstruction management table is provided to reconstruct management table loss or damage caused by power outage or irregular shut-down of the computer and will be able to provide flash memory on the hard disk cache control.