A ratchet driving mechanism for a hand tool includes: a drive unit, including a drive shaft, a position member and a plurality of latch members, wherein each of the latch members includes a latch plate and an elastic piece; an adjustment ring, sleeved on the drive shaft and formed with a plurality of cavities allowing the position member to be selectively latched and positioned and an accommodation slot allowing each of the latch plates to inwardly/outwardly move; and a ratchet unit, sleeved on the drive shaft and formed with a plurality of ratchet teeth allowing each of the latch plates to be engaged. Accordingly, during the drive shaft driving the ratchet unit for generating rotation, the position member is able to precisely position the ratchet unit on drive shaft.