The invention introduces a method for priority writes in an SSD (Solid State Disk) system, performed by a processing unit, including at least the following steps. After a priority write command instructing the processing unit to write first data whose length is less than a page length in a storage unit is received, a buffer controller is directed to store the first data from the next available sub-region of a buffer, which is associated with a priority write, in a first direction. After a non-priority write command instructing to write second data whose length is less than page length in the storage unit is received, the buffer controller is directed to store the second data from the next available sub-region of the buffer, which is associated with a non-priority write, in a second direction.