The invention discloses a data backup method, a flash memory controller and a flash memory storage system. The data backup method is used for backing up data temporarily stored in a cache of a flash memory storage device, wherein the flash memory storage device is provided with a plurality of solid units. The data backup method comprises the following steps of: logically grouping a part of the solid units into a data zone and a fast fetching zone; judging whether a triggering signal is received; and when receiving the triggering signal, copying the data stored in the cache to the fast fetching zone. Therefore, the data backup method can be used for fast writing the data temporarily stored in the cache to the solid units so that the problem of timeout is avoided.