A F type clamp having a locking function includes a base frame including a locating frame bar and a rail, a sliding member having one end coupled to the rail and selectively set between a locking position and an unlocking position, a clamping member movably mounted at an opposite end of the sliding member and providing a jaw plate for working with the locating frame bar to hold down a workpiece, and a locking device set between the sliding member and the rail for locking the sliding member to the rail under normal conditions and for enabling the sliding member to be moved relative to the rail by an external force.