Abstract: An air-flow control valve device for a helmet is disclosed. The valve device provides the effect of a warm during the winter and cold effect during the summer. The device is adjustable in accordance with the temperature change so as to provide air-flow and maintain warm. During the summer, the moveable valve gate is pushed forward, and the air within the helmet flows out of the helmet via the gap between the valve gate and the rain-blocking plate. During the winter, the valve gate is pushed backward to seal with the rain-blocking plate to effect the blocking of the heat to release from the helmet. Further, a warmth-keeping member is provided at the frame edge of the helmet to prohibit cold air to enter so as to fully prohibit cold air to enter the head portion and to maintain the warm air from releasing.