A tripod has an outer tube, a central tube, an inner tube, two positioning pins, a connecting joint, a knob, a clamping device and a leg set. The outer tube, the intermediate tube and the inner tube are sequentially socketed. The inner tube has a first engaging disk with a through aperture. The connecting joint extends above a locking rod and has a second engaging disk with a bolt. The knob is provided with a threaded aperture. The clamping device has a back member and a side member, and a first locking aperture and a second locking aperture are respectively provided on the back member and the side member. The supporting legs are provided on the leg set, each of the supporting legs has a first surface and a second surface, and the second surface is provided with a recess containing a pivotal grounding nail.