In order to clarify the impact of urban surface changes on the temporal and spatial changes of urban thermal environment caused by urbanization, using the radioactive transfer equation algorithm and the ISODATA unsupervised classification method, the land surface temperatures were retrieved and land use classification were carried out, based on remote sensing images of 2002, 2008 and 2014. In addition, the vegetation coverages of the land surface were calculated by the NDVI dimidiate pixel linear model. Finally, through the statistical analysis and comparative analysis of the temporal and spatial changes of land use, vegetation cover and thermal environment in the study area, the following results were obtained: (1) In 2014, the urban land-use areas had increased by 295.18 km~2, 1.62 times more than 2002, and the proportion had increased by 10.98%. (2) A large number of medium-low vegetation coverage areas had been converted to medium-high vegetation coverage areas, and the regions of vegetation coverage greater than 0.6 had increased by 220.26 km~2. (3) The medium-high temperature areas increased continuously with a total increase of 841.78 km~2; meanwhile, the areas of low temperature and medium-low temperature were decreased by 701.71 km~2. And (4) although the urban thermal environment was affected by the surface characteristics such as vegetation coverage, the temperature of urban continuous increase was not only caused by urbanization, but also by global warming. The research results can be used as an important scientific basis for space optimization and planning, which will help to improve the urban thermal environment and relieve its negative effects. This study may also be a valuable reference for city development strategy planning of Kunming in future.