The invention discloses a cantilever type gravitational energy power generation device, and relates to power generation devices. The device is designed for solving the problems that at present, wind energy power generation is not stable, hydroelectric power investment is high, and thermal power generation pollutes environment. The device comprises a rotating shaft, the rotating shaft is matched with a bearing in a bearing pedestal for mounting, multiple rotating arms are arranged on the rotating shaft, each rotating arm comprises a fixed arm, the fixed arms are fixed to the rotating shaft, telescopic arm drive motors are connected to the fixed arms, telescopic arm drive screws are arranged on power output shafts of the telescopic arm drive motors, a rear supporting plate is fixed to a telescopic arm, the rear supporting plate is in threaded connection with the telescopic arm drive screws, a balance weight sliding block drive motor is arranged on the telescopic arm, a balance weight sliding block drive screw is arranged on an power output shaft of the balance weight sliding block drive motor, and the balance weight sliding block drive screw is in threaded connection with a balance weight sliding block. A fixed balance weight block is fixed to the front end of the telescopic arm. The balance weight sliding block drive screw is matched with a bearing in a front supporting plate for mounting. The advantages of being small in investment, energy-saving and environment-friendly are achieved.