Abstract: With the urban development, replanning and reconstruction of the old urban area have become key issues of the urban development. Over the past decade, Fuzhou City of Fujian Province, Southeast China, has paced up its reconstruction progress. The Cangxia District, located in the southwestern Fuzhou, was therefore replaned and reconstructed to improve people’s living conditions because the area was full of intensively-built shanties. In order to study the thermal environmental changes of the Cangxia District before and after the reconstruction, three Landsat TM images of 1986, 1996 and 2006 were utilized to perform feature extraction of thermal-related information of the area, such as land surface temperature (LST), impervious surface area and vegetation coverage. The quantitative analysis on the relationship between impervious surface and LST suggested there is a positive exponential relationship between the two factors. With the assistance of the Urban-Heat-Island Ratio Index (URI), digital image processing on the three multi-temporal images has revealed the spatial and temporal variations of the urban heat island effect (UHIE) in the study area from 1986 to 2006. The results show that after the launch of the reconstruction project for the shanty-dominated area, the UHIE in the area has been greatly mitigated. In the past 20 years, the URI has been decreased from 0.648 in 1986 to 0.245 in 2006 owing to the significant decrease in high-density impervious surface areas and notably increase in vegetation covers. Obviously, the reconstruction is beneficial to the UHI mitigation of the Cangxia District.