Abstract: To explore new practical means of alleviating the negative effect of heat stress on rice plants during the heading-flowering stage, a field experiment was conducted in Ji’an, Yugan, and Nanchang counties of Jiangxi Province from 2017 to 2018 with three indica hybrid rice varieties. Under ambient high temperature condition during the heading-flowering period, we sprayed five concentrations of salicylic acid (SA) (SA₁-SA₅: 100, 500, 1000, 1500, 2000 μmol·L^-1) and five concentrations of KH₂PO₄ (K₁-K₅: 7.35, 14.70, 22.05, 29.40, 36.75 mmol·L^-1) on the leave of rice, with deionized water as the control (CK), to mesure the physiological characteristics and grain yield. The results showed that compared to CK,plants treated with SA and KH₂PO₄ had higher chlorophyll content, soluble sugar content, soluble protein content, proline content, supero-xide dismutase activity, and peroxidase activity, but a lower malonaldehyde content, among which SA₂ and K₃ treatments performed the best. The treatments of SA₂, SA₃, K₃, and K₄ increased the number of grains per panicle, seed-setting rate, and grain yield, with the effects of SA₂ and K₃ treatments being significant. Compared to CK, the SA₂ treatments enhanced the number of grains per panicle, seed-setting rate, and grain yield by 7.0%, 4.0%, and 11.9%, respectively; the K₃ treatments enhanced the number of grains per panicle, seed-setting rate, and grain yield by 3.9%, 4.7%, and 6.6%, respectively. The optimal measure was spraying 500 μmol·L^-1 SA or 22.05 mmol·L^-1 KH₂PO₄, which could significantly increase grain yield of single-season rice under high temperature condition during the heading-flowering period.