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 .