A data writing method, a memory control circuit unit, and a memory storage apparatus are provided. The method includes recording a flush command counting (FCC) value, and updating the FCC value whenever receiving a flush command from a host system. The method further includes getting a first physical erasing unit as an active physical unit and determining whether the FCC value is greater than a FCC value threshold. The method further includes setting a writing mode of the active physical unit as a first writing mode if the FCC value is greater than the FCC value threshold, and setting the writing mode of the active physical unit as a second writing mode if the FCC value is not greater than the FCC value threshold.