The abnormal heat island (AHI) effect has recently been reported in several karst cities. However, the combined effect of the abnormal and urban heat island (UHI) effect is still a gap. This study analyzed the combined effect the AHI and UHI in Guiyang, a typical rapidly urbanizing karst mountain city, to provide insights into the variation and formation of AHIs and UHIs using Landsat imagery. Although the AHI effect remained the major component of the thermal environment, the impact of UHI intensified with rapid urbanization. Moreover, in addition to suitable topographic conditions such as shallow slopes and high elevations in sunny aspects, the low and low-medium vegetation coverage lands were highly related to the formation of the AHI, and the AHI intensity increased in almost all directions with urban expansion. In addition, the formation conditions and mechanism of the AHI can be attributed to the unique thermal properties of karst carbonate. The above results suggest that karst rock desertification is the key point for the improvement of the regional thermal environment, so comprehensive prevention of rock desertification and rational planning of construction projects should be involved in environmental protection in karst mountain cities.