The invention discloses an automatically stretching type vertical-axis wind driven generator comprising a generator, a spindle, a spoke, vanes, a support rib and a screw rod. The screw rod is mounted on the spindle which is connected with the generator, and the vanes are mounted on the spindle through the spoke and connected with the screw rod through the support rib. The automatically stretching type vertical-axis wind driven generator further comprises a support frame, a heavy ball, a gear, an inner sleeve, an outer sleeve, an inner brake and an outer brake, when the wind speed is too high, the heavy ball locks the outer sleeve, the gear drives the screw rod to move downwards, the vanes close up, and the outer brake limits the displacement of the screw rod; when the speed is too low, the heavy ball lock the inner sleeve, the gear drives the screw rod to move upwards, the vanes expand, and the inner brake limits the displacement of the screw rod. The automatically stretching type vertical-axis wind driven generator is driven without a motor, vanes' sweeping area is decreased automatically when wind speed is too high and increased automatically when wind speed is too low, the generating capacity of the vertical-axis wind driven generator is increased, safe and stable running of the vertical-axis wind driven generator is guaranteed.