A flash memory initialization method executed by a flash memory initialization device to initialize a flash memory device having a flash memory and a flash memory controller includes: determining an acceptable maximum number N of candidate addresses; determining a number M of different capacity sizes; classifying the candidate addresses into M portions; determining a difference value between two address values of any two adjacent addresses among the m-th portion of candidate addresses; determining multiple address values of the m-th portion of candidate addresses according to the difference value; and determining actual addresses of the m-th portion of candidate addresses according to the multiple address values; and controlling the flash memory controller to write the boot up information into at least one storage location corresponding to at least one of the m-th portion of candidate addresses according to the actual addresses.