The invention discloses application of an SPL18 gene in enhancing plant yield. The SPL18 gene is derived from corn, rice, sorghum, wheat, barley, rye, millet, soybean, rape or sunflower. For the first time, the invention provides a method for enhancing grain number per spike or/and grain weight by promoting spike branching by using the SPL18 gene. The SPL gene is overexpressed in the crop, thereby effectively promoting spike branching, enhancing the grain number per spike or/and grain weight by 3% or above, and increasing the yield by 5% or above. The technique can effectively enhance the individual yield and yield per unit area, thereby enhancing the grain productivity and providing a new idea for national grain safety.