A data storage device with flash memory and a flash memory control method are disclosed, which upload the physical-to-logical address mapping information of one block to the flash memory section by section. A microcontroller is configured to allocate a flash memory to provide a first run-time write block. Between a first write operation and a second write operation of the first run-time write block, the microcontroller updates a logical-to-physical address mapping table in accordance with just part of a first physical-to-logical address mapping table. The logical-to-physical address mapping table is provided within the flash memory. The first physical-to-logical address mapping table is established in the random access memory to record logical addresses corresponding to physical addresses of one block.