Abstract: 【Objectives】 Boron, one of the essential trace element for plant growth and development, has special function on the normal development of pollen tube elongation and fertilization process. This study explored influences of applying boron on floral development and grain-setting for providing references to the chemical regulation of increasing the number of grains per spike and the yield. 【Methods】 Field experiments were conducted in the Science and Technology Demonstration Park of Henan Agricultural University during the 2012-2013 and 2013-2014 growing seasons. Wheat cultivar Yumai 49-198 was chosen for test material and 0.2% borate solution was foliar sprayed 25 days after the jointing stage(S1), with water as control(S0). EMZ-TR dissecting microscope was used to observe and record the young spikelets differentiation process in the main stem, and that of differentiation of young spikelet at different stages. At the maturity period, the grain number in spikelet at basal, central, and apical of wheat plant, and those in each spikelet at different floret positions were counted.【Results】The grain-setting rates of fertile floret on the basal and central spikelet of wheat sprayed with borate were increased by 5.85% and 12.55% respectively, compared with control, the florets degeneration rates at the basal spikelet were decreased by 7.47%, and the infertility rate is decreased by 20.07%. The florets degeneration rate at the central spikelets of the borate treatment is decreased by 12.06% and the infertility rate is decreased by 35%. The significant decrease in the degeneration and infertility rate by borate was mainly happened in the basal and central spikelet floret, not in the apical spikelet floret. Further analysis showed that the boron spraying could significantly promote florets grain-setting at different floret positions of different spikelets, especially promote seeds of the fourth floret position which is weak floret.【Conclusions】The degeneration rates of florets and the abortion rates of fertile florets at basal and central spikelet positions can be significantly reduced by spraying boron at the 25 days after the jointing stage, as a result, improving the grain-setting rates of single spike and getting the more grain number.