The invention discloses a power supply system of a wireless drilling inclinometer underground instrument. The power supply system includes a direction-varying stator and a magnetic force rotor which are axially arranged, the magnetic force rotor is coupled with a magnetic force main shaft, the magnetic force main shaft is connected with a magnetic force flange, the magnetic force flange is axially opposite to a coil group but is not in contact with the coil group, the coil group is connected with a regulation circuit, and the regulation circuit is connected with an instrument power supply bus; the surface of the direction-varying stator is provided with an inclined blade, and the inclination angle is adjustable; the magnetic force flange and the coil group has a certain adjustable gap; and the regulation circuit contains a judgment circuit and a voltage stabilizing circuit, and electricity generated by the coil group is judged by the judgment circuit, and is output in a voltage range suitable for the instrument after voltage stabilization by the voltage stabilizing circuit. The power supply system of the wireless drilling inclinometer underground instrument can realize electricity generation output in a 10L/S to 70L/S mud displacement range.