A data allocating method includes steps of: determining whether data to be written into a physical memory block is hot data or cold data; when the data is hot data, according to a hot data allocating order, searching at least one first empty sub-block from the physical memory block to allocate the data; when the data is cold data, according to a cold data allocating order, searching at least one second empty sub-block from the physical memory block to allocate the data.