The invention relates to motor train unit sand feeding and provides a combined changeover valve, a sand feeding device and a CRH motor train unit automatic sand feeding trolley. The combined changeover valve comprises a valve body, and a sand sucking valve, a sand feeding valve and a negative-pressure control valve are arranged on the valve body. The valve body is provided with a sand sucking opening and a sand outlet, and the sand sucking valve controls connection and disconnection of the sand sucking opening and the sand outlet. The valve body is further provided with a first air inlet and a first air outlet, and the negative-pressure control valve controls connection and disconnection of the first air inlet and the first air outlet. The valve body is further provided with a second air outlet and a second air inlet, and the sand feeding valve controls connection and disconnection of the second air outlet and the second air inlet. The sand feeding device is further provided and comprises the changeover valve. The sand feeding trolley is further provided and further comprises the sand feeding device. In the changeover valve, the sand sucking valve, the sand feeding valve and the negative-pressure control valve are integrated on the valve body, and the valve body can be used in cooperation with a sand tank and an air blower to achieve sand sucking and sand outflow; and operation is convenient, and maloperation and neglected operation of workers are not likely to happen.