1. A data accessing method, for a flash memory storage device having a data perturbation module and a flash memory, wherein the flash memory has a plurality of physical pages corresponding to a plurality of logical pages, the data accessing method comprising: receiving a read command from a host, wherein the read command indicates reading data from a first logical page among the logical pages and the first logical page corresponds to a first physical page among the physical pages; determining whether the first logical page or a first physical page corresponding to the first logical page among the physical pages has been written with data; and transmitting a predetermined data to the host if the first logical page or the first physical page has not been written with data; decoding data read from the first physical page corresponding to the first logical page by the data perturbation and transmitting the decoded data to the host if the first logical page or the first physical page has been written with data.