Abstract: How to analyze distributional characteristics of urban thermal space and its quantificational relations with land use/cover is one of the difficult problems. Many methods can be used to study the urban heat island. Remote sensing dominates over traditional research methods because of speediness, impersonality, ninety, macroscopical feature, strong periodicity so that remote sensing becomes a kind of good tool to study urban heat island. The paper analyzed space distributional rules and the cause of formation of urban thermal space in Nanjing by using Landsat ETM⁺ of 2002 and established land cover index based on the relations between LST and NDVI. The result indicates that there are three centers of heat island in Nanjing, mainly in industrial region, not in commercial or residential areas. The spatial distribution pattern of land use/cover affects wholly the distributional pattern of the urban heat space; the difference of surface material's thermal and biologic feature is the essential reasons of surface temperature, because of different surface materials with different heat capacity, heat conductivity, inertia and NDVI; industrial heat has important effect on heat island. The partitioning of sensible and latent heat fluxes and, hence, surface radiant temperature response is modulated both by surface soil content and vegetation cover. The surface radiant temperature response is a function of varying vegetation cover and surface soil water content. The land cover index (LCI) can reflect surface soil water content and vegetation cover, explain the essential reasons that each land use/cover contributes differentially to urban heat island. Such an index can allow changes in land use at neighborhood-scale to be input in the initialization of atmospheric and hydrological models, as well as provide a new approach for urban heat island analysis. The LCI of urban land use is smaller than the LCI of water, forest and cropland. LCI is smaller; the intensity of urban heat island is stronger. For a special region, LCI will increase gradually per unit with higher urbanization level.