The invention discloses a gene OsPK3 for controlling 1000-grain weight of rice. The nucleotide sequence of the gene is the nucleotide sequence which is shown in SEQ ID NO:2, or the nucleotide sequencewhich is shown in the SEQ ID NO:2 and can encode the same functional protein by substituting, deleting and/or adding one or more nucleotides. According to the gene OsPK3 for controlling the 1000-grain weight of the rice, a new gene OsPK3 is positioned through a map-based cloning method, and a transgenic mutant strain is formed by knocking out the gene OsPK3 by utilizing a CRISPR/Cas9 system; whenthe mutant plant is compared with a wild type, the seed grain thickness is decreased, the 1000-grain weight is remarkably reduced, and the plant height is reduced, which show that the gene is the gene for controlling the 1000-grain weight of the rice and can be used for high-yield and stable-yield breeding of the rice.