The invention discloses a grain storage barn. The grain storage barn comprises a storage barn body, a sampling detection component and a freshness keeping component, wherein the storage barn body comprises a granary and a transportation barn, the transportation barn and the granary are separated by a cylindrical division plate, a flood dragon shaft is vertically installed in the transportation barn, and an inner wall of the transportation barn is further provided with an electric heating plate; the sampling detection component comprises a sampling barrel, a second motor, a slipway and a moisture detector, the freshness keeping component comprises a nozzle, a spray pipe, a material drawing pump and a storage box, and the nozzle is arranged at the top of the transportation barn, directly faces an opening at the top of the division plate, and is connected with the spray pipe. An independent transportation barn is arranged in the grain storage barn, the flood dragon shaft is utilized to circularly transport grain, heating, drying and spraying a freshness keeping agent are carried out on the grain when the transportation is conducted, the grain in the storage barn can be kept dry over a long period of time, the grain freshness is maintained for a long time, the whole system runs automatically, the human power is not required, and the human resources are saved.