A memory storage device and a read/write method thereof, first defining logically the flash memory as at least one particular data management area and at least one common data management area; next, determining the logical block address located in the particular data management area or the common data management area according to data transmitted to an external system by an area decision mechanism, wherein the method of writing to the particular data management area is by using a method of dynamic deviation value, and the method of writing to the common data management area is by using a method of same displacement value. Whereby, the particular data management area can be avoided moving frequently caused by updating data from the external system to improve read/write performance of the flash memory.