The invention discloses a grain steaming device and a grain steaming method. The grain steaming device comprises a grain steaming system controlled by a computer, and a connecting system, wherein the grain steaming system comprises a grain steamer provided with a steam inlet end and a steam outlet end, and the grain steamer is provided with a feeding hole; the connecting system is communicated with the steam inlet end and the steam outlet end of the grain steamer; and the connecting system is provided with a three-leaf Roots steam compressor electrically connected with the computer. The connecting system is utilized for communicating the steam inlet end with the steam outlet end of the grain steamer, the computer controls the whole grain steaming process and detects the temperature and pressure of steam in the grain steamer, the three-leaf Roots steam compressor compresses the steam for recycling, and the steam is guided into the grain steamer for cyclic utilization, so that the automation degree of the grain steaming device is improved, the waste of energy is avoided, and the production cost is reduced; and the grain steaming device disclosed by the invention is a large-sized micro pressure grain steaming device which can reduce the quantity of devices, avoid annual inspection and further reduce investment and maintenance costs.