As the second largest forest region in China,the ecological environment of the southwest forest area is fragile and highly sensitive to climate change. In recent years,forest carbon sequestration has undergone changes and has attracted significant attention due to the impact of climate and environmental factors. Thus,studying the spatiotemporal dynamics and influencing factors of carbon sequestration capacity in southwest China's forests against the backdrop of climate change is significant. By using the soil respiration model and the Terrestrial Ecosystem Carbon flux (TEC) model,combined with meteorological and remote sensing data,we estimated the net ecosystem productivity (NEP) in the forest of southwest China from 2001 to 2021. And trends in NEP variation and its sustainability were analyzed using Theil-Sen slope estimation,Mann-Kendall mutation test,and Hurst index. Furthermore,methods including partial correlation analysis,geographical detectors,etc. were employed to quantitatively evaluate the influence of climate and environmental factors such as temperature,precipitation,aspect,and slope on forest NEP. The results indicated that: (1) The average annual NEP in the forest of southwest China was 333.8 g C m^-2 a^-1(3.338 t C hm^-2 a^-1),indicating an overall carbon sink. From 2001 to 2021,forest NEP in southwest China showed a fluctuating growth trend,increasing by an average of 3.9 g C m^-2 a^-1(0.039 t C hm^-2 a^-1) annually. Areas with a significantly increasing NEP trend accounted for 33.2% of the total forest area,predominantly in northern Sichuan and southwest Yunnan. Deciduous broad-leaved forest and forest areas in Guizhou province showed the highest NEP increases,averaging 4.5 g C m^-2 a^-1(0.045 t C hm^-2 a^-1) and 5.9 g C m^-2 a^-1(0.059 t C hm^-2 a^-1) per year,respectively. (2) From the perspective of change persistence,the Hurst index of NEP in most forest areas was less than 0.5,indicating that future NEP trends might reverse the past patterns. Forest NEP in southwest China is projected to show a decreasing trend in the future. The proportion of forest areas where NEP shifts from an increasing trend to a decreasing trend accounted for 64.6% of the southwest forest area. However,30.5% of the forest areas showed an increasing trend in NEP for the future,with the largest distribution in Yunnan (57.1%),followed by Sichuan (36.2%). (3) From a temporal scale impact analysis perspective,analysis of temporal impacts revealed a negative correlation between NEP and precipitation and a positive correlation with evapotranspiration and temperature over the past 20 years in most forest areas of southwest China. Evapotranspiration was identified as the primary climatic factor influencing NEP in forest areas,accounting for 67.2% of the total area,followed by precipitation (21.3%) and temperature (6.1%). Differences in key climatic factors affecting NEP were noted among different forest types. Precipitation primarily affected the NEP of shrub and evergreen broad-leaved forests,while temperature primarily affected coniferous forests in Guizhou province. (4) From a spatial distribution impact analysis,the influence of climatic and environmental factors on carbon sequestration function appears quite complex. Temperature,radiation and elevation are identified as the top three factors with the strongest explanatory power for the spatial variations in NEP in the southwest forest region. However,in the forest regions of Guizhou and Chongqing,each factor shows significantly weaker explanatory power (q < 0.1),indicating a more intricate driving mechanism of climatic and environmental factors on NEP spatial distribution in these forest areas. Additionally,there are interactions among various factors influencing the spatial distribution of forest NEP in southwest China,characterized by dual-factor enhancement and nonlinear enhancement effects. The most significant interaction factors were observed in temperature∩sunshine (q=0.33),radiation∩evapotranspiration (q=0.31),and temperature∩radiation (q=0.29),indicating that these interaction factors play a dominant role in influencing the spatial distribution of NEP in the southwest forest region. The findings of this study will help reveal the response mechanism of forest NEP to climate and environmental changes,providing fundamental data support for ecological protection and carbon neutrality research in southwest China.