The invention discloses an automatic height measurement device for crops. The device is used for automatic measurement of crop height. The device comprises a pedestal, a transmission part, a sensing part, a control part and a display part; the transmission part, the sensing part, the control part and the display part are arranged on the pedestal; the control part sends instructions to control theoperation of the transmission part and drives the sensing part to scan and measure the crops so as to acquire measurement data, and the sensing part returns the measurement data to the control part; and the control part calculates and processes the returned measurement data to acquire the crop height, and outputs the crop height to the display part to display. The device can accurately determine the canopy tops of the crops at the same time of ensuring low hardware cost and finish automatic measurement of the crop height.