A data accessing method for a flash memory and a storage system and a controller using the same are provided. The data accessing method includes grouping a plurality of physical blocks of the flash memory into a data area, a spare area, and a random area and when a write command and a new data to be written are received from a host, determining whether the new data is a continuous data, wherein the new data is written temporarily into the physical blocks in the random area if the new data is not a continuous data. Thereby, the number of data moving and physical block erasing is reduced and accordingly the data accessing speed in a random writing mode is increased.