A method for soft configuring communication a memory device to act as a Key Card that can switch on or off some particular functions of either an application program or the memory device itself. The method comprising the steps of: connecting the memory device to an external device; running a specific application program on the external device, the application program writing and storing a specific data into the memory device, the specific data including at least a command and a key; the memory device generating a response value according to the command and key of the specific data; and the external device reading the response value from the memory device and checking a status of the response value; if the response value is checked to be valid, then the application program will be able to access the memory device by using functions defined by the command; if the response value is checked to be invalid, then functions of the application program will be restricted.