Abstract: A security system for a flash memory and a method thereof are disclosed. The method of security system for a flash memory, includes the steps of a) providing a predetermined limit signal for a host system; b) defining a specific signal stored in the flash memory installed with a identification program for indicating a capacity of the flash memory; c) comparing the specific signal with the predetermined limit signal while the flash memory is connected to the host system; d) inhibiting access to the identification program of the flash memory if the specific signal does not correspond to the predetermined limit signal, but a residual space of the flash memory is available.