A data buffering method used when performing a read operation on an optical storage medium is disclosed. After a first data unit having an unidentifiable and temporarily undeducible ID address is reproduced through the read operation, the method starts storing the first data unit and subsequently reproduced data units into a buffer memory in turn. After a second ID address of a second data unit of the subsequently reproduced data units is identified, the method deduces a target memory address of the buffer memory according to the second ID address and a target ID address. A buffer start pointer is then set according to the deduced target memory address.