A data writing method for a rewritable non-volatile memory module having a plurality of physical erasing units, and a memory control circuit unit and the memory storage apparatus are provided. The method includes grouping the physical erasing units into at least a data area, a backup area and a spare area; and setting a value obtained by summing a minimum threshold and a predetermined number as a garbage collecting threshold. The data writing method also includes getting at least one physical erasing unit from the spare area, writing data into the gotten physical erasing unit, associating the gotten physical erasing unit with the backup area and re-adjusting the garbage collecting threshold according to the number of physical erasing units associated with the backup area and the minimum threshold.