The invention provides a vehicle-mounted drier. The vehicle-mounted drier comprises a drying bin, a heating bin, a support, an auger elevator, a vacuum unit, a heating device, a heat conduction tube,a heat conduction tube and a heat circulation pump. The drying bin and the auger elevator are installed in a bin of the heating bin. The heating device is connected with a heat energy inlet and a heatenergy outlet of the heating bin through the heat conduction tube. The drying bin comprises a bin body, a heat exchange device, a discharging valve, a feeding hopper and a heat exchange device, wherein the heat exchange device is installed in a bin of the drying bin, and an exhaust port at the upper end of the drying bin is connected to the vacuum unit through an air guide tube. The grain harvester is provided with a vehicle-mounted dryer and can be used for drying harvested cereals while the cereals are harvested, and a heat conduction medium for carrying heat energy in the vehicle-mounted dryer directly conducts heat conduction to the grains through a heat pipe, so that the heat conversion efficiency is high, the loss is small, the three-dimensional heat exchange heat conduction is adopted by the heat exchange device of the drying bin, the heat conduction heat exchange speed is improved, the vacuum drying time is shortened, and the drying time of the grains is shortened.