The invention discloses a nutrition agent for increasing yield of grain crops and a preparation method. The nutrition agent is composed of nucleotides, 5-ribose phosphate, boron and a diffusion agent. The preparation method comprises mixing the nucleotides, the 5-ribose phosphate and the boron with stirring, and then adding the diffusion agent under normal temperature to prepare the agent. The nutrition agent has advantages of good water-solubleness, easy absorption and utilization for the crops, simple usage, small application amount, stable performance and long shelf-life, can not only provide nucleic acids, trace element boron and other nutrients necessary for rice and other main food crops after flowering, but also inhibit photorespiration consumption of the crops, and is remarkable in yield increasing for the rice and other food crops and good in economic benefit.