Abstract: A method for retarding the duplication of data-storage device, by which the main program of the software in the data-storage device is hard to duplicate. The inventive method uses a processing program to access data in a base of specific prime number determined by the software developer. The original main program in software to be protected is encoded and then linked with the processing program to form a composite, which will initialize an examining procedure. Moreover, a plurality of checking codes are added into the composite program. The feature of data assessing in a base of specific prime number and the incorporation of checking codes can retard the attempt of copying.