The invention discloses an automatic grain vending machine. The vending machine comprises a machine case, a case door on one side of the machine case and grain storage warehouses in the machine case, and a stock taking warehouse is arranged on the case door; each grain storage warehouse comprises a warehouse body, a feeding port in the upper portion of the corresponding warehouse body and a weighing hopper on the lower portion of the corresponding warehouse body; a discharging port is formed in the bottom of the corresponding weighing hopper, a discharging valve is arranged in the corresponding discharging port, and a weight sensor is arranged in the corresponding weighing hopper; discharging channels which are communicated with the stock taking warehouses are formed below the discharging ports; vacuum orifices are formed in the warehouse bodies and are communicated with a vacuum pump in the machine case through pipes; an air inlet is further formed in the corresponding warehouse body, and an air inlet valve is arranged in the corresponding air inlet. The automatic grain vending machine solves the problems of storage, freshness retaining and quality retaining of grain in the vending machine, can make customers purchase fresh grain anytime more conveniently and rapidly, and can also avoid waste of cereal resources due to improper storage.