The invention belongs to the technical field of molecular biology and particularly relates to use of a rice three-flower spikelet gene LF1 in the increase of the yield of gramineous food crops. The invention further provides the use of the rice three-flower spikelet gene LF1 in the increase of the yield of the gramineous food crops and a preparation for increasing the yield of the gramineous food crops. According to the use, the gene LF1 is separated and causes ectopic expression due to the mutation of a microRNA165/166 regulatory site, so that two ''lateral florets'' in a spikelet are restored, and the number of the florets of the spikelet of an lf1 mutant reaches 3 (named as a ''three-flower spikelet'') together with an original acrogenous fertile floret. A new breeding way for increasing the kernel number per spike is provided and is of a very important significance to the further increase of the yield of the rice. A new choice is provided for the increase of the yield of the gramineous food crops.