Abstract: Taking the main urban area of Kunming as the research object, based on LandsatTM/OLI remote sensing images of three periods in 2000, 2010 and 2020, the surface temperatures in three periods were inversed. The temporal and spatial evolution of the thermal environment effect was analyzed with the standard deviation ellipse, and the influencing factors of thermal environment effect were discussed by the geographic detector. The results showed that in the recent 20 years, the heat island areas in the main urban area of Kunming had been concentrated in those with intensive urban construction, and the main axis of the thermal environment direction had changed from northeast-southwest to northwest-southeast. In the early stage, the center of the thermal environment deflected 57.5° to the northwest and shifted by 2.47 km, and in the later stage, deflected 24.25° to the northwest and shifted by 0.86 km. There was a trend of transition from extremely low-temperature zone to low-temperature zone and relatively low-temperature zone, and from relatively high-temperature zone and high-temperature zone to extremely high-temperature zone. Among them, the enhancement trend of the thermal environment effect in Guandu District was the most significant. The building lot and fractional vegetation cover (FVC) had the greatest influence on the surface temperature. The influence on the surface temperature would be increased when the interaction between building lot and elevation. And the interaction between water and building lot or impermeable surface would weaken the mitigation effect of water on the thermal environment effect.