The invention relates to a cooling and blowing device for a radar level gauge and a material level detection system. The cooling and blowing device comprises a first branch circuit which is provided with a flow regulating valve and a first opening and installed on a sealed container, a second branch circuit which is provided with a reducing valve and a second opening and installed on the side wallof the sealed container, a main circuit connected with air inlets of the first branch circuit and the second branch circuit so as to receive gas, a differential pressure transmitter and a controller,wherein two pressure measuring openings of the differential pressure transmitter are connected with the first opening and the second opening respectively, and the controller is connected with the differential pressure transmitter and the flow regulating valve. The controller can regulate the opening of the flow regulating valve according to a detection value of the differential pressure transmitter, the air outlet of the first branch circuit cools and blows the transceiving end of the radar level gauge so as to lower the influence of gas with high temperature, dirt, moisture and pressure inside the sealed container on the radar level gauge, pressure changes of the air outlet of the first branch circuit are in positive correlation with pressure changes inside the sealed container, and therefore the purpose of lowering energy consumption is achieved.