A driving system for a core drilling rig has a driving motor. The driving motor has an outer rotor and an inner stator, and mutually-matched convex ribs are provided on the inner wall of the outer rotor and the outer wall of the inner stator. The outer rotor and the inner stator are in clearance fit. A clearance between the outer rotor and the inner stator is a driving liquid channel. The length of the outer rotor is less than that of the inner stator. The outer rotor is provided between the front and rear ends of the inner stator. The outer rotor is connected to an outer cylinder. The rear end of the inner stator is connected to a coupling.