Abstract: Field experiments was conducted on the effects of different irrigation depths on heat damage during grain filling period of early rice from 2021 to 2022. During the grain filling period of early rice suffering from heat damage above 35.0 ℃, 4 experimental treatments including 0, 2~3, 5~6, and 8~10 cm irrigation were respectively carried out at 3 interval of sowing, and the flag leaf surface temperature, chlorophyll content, photosynthetic rate, panicle air temperature, 1000-grain weight were measured during heat damage period of early rice under different irrigation treatments. The results showed that compared to 0 cm irrigation(CK), 2~3, 5~6, and 8~10 cm irrigation could decrease flag leaf surface temperature by 0.16~0.30 ℃, and the leaf temperature decreased with the increase of the irrigation depth. Different Irrigation depths had no significant effects on the panicle air temperature the leaf temperature decreases as the irrigation layer increases. Irrigation is beneficial for the increase of chlorophyll content, but not significant. The 2~3 cm irrigation can increase photosynthetic rate by 1.2~3.8 μmol CO₂/(m²·s), and 1000-grain weight by 0.17~0.41 g, which has the best effect on defending against heat damage during grain filling period of early rice.