The invention discloses a processing method of precooked coarse grains simultaneously boiled and cooked with rice, and belongs to the technical field of deep processing of agricultural products. The method comprises the following steps: screening mixed beans or coarse grains as a raw material, cleaning, immersing, carrying out fumigating precuring treatment on the raw material by using steam to obtain a precooked raw material, carrying out loosening and microwave slaking alternative treatment on the precooked raw material, cooling, and packaging to obtain precooked coarse grains. The method has the advantages of low production cost of the processing process, short processing period, and products processed through the method have the characteristics of maintenance of the original appearance form, less nutrition component loss, maintenance of the original smell of coarse grains, storage and transportation benefiting, and adaptation to the industrialized popularization.