Abstract: The effect of different gap sizes on soil respiration in a Pinus massoniana plantation in Parallel Ridge Valley area of eastern Sichuan Province was discussed, which could provide a theoretical basis for sustainable gap modification strategy of plantations. The Pinus massoniana plantation in Dongfanghong Forest Farm of Huaying City was selected as the research object, and three levels of gap sizes (closed canopy: CK, 200 m² small gap: S, 600 m² large gap: L) were set. From July to August 2021, soil respiration and its components were measured by Li-8100A soil carbon flux system, and the atmospheric temperature (T), atmospheric moisture (M), atmospheric pressure (P) and atmospheric CO₂ concentration (C_a) were measured in combination with temperature and moisture probe. The results showed that: (1) Compared with the L treatment (4.29 μmol·m⁻²·s⁻¹), S treatment (5.99 μmol·m⁻²·s⁻¹) could promote the soil respiration significantly (P<0.05). (2) S treatment could significantly increased the atmospheric temperature, but the atmospheric moisture within L treatment was significantly lower than CK (P<0.05). (3) Compared with CK, soil mineral respiration rates significantly increased in S treatment but decreased significantly in L treatment, while the root respiration rate increased significantly in S and L (P<0.05). (4) The correlation analysis indicated that there was extremely significant and positive correlations between the soil respiration and atmospheric temperature (r=0.786), and the fitting regression equation indicated that atmospheric temperature had a significant direct and positive effect on soil respiration, and had an indirect positive effect on soil respiration by changing soil mineral respiration and root respiration. In conclusion, the formation of small gaps in Pinus massoniana plantations in Parallel Ridge Valley area of eastern Sichuan Province could significantly increase soil respiration rates, and the atmospheric temperature was the main factor that affecting soil respiration after the formation of forest gaps.