Urban thermal environment has had a far-reaching impact on local climates and on the quality of living environments.Distinct differences between urban areas and surrounding rural areas have been widely observed; this phenomenon is called the Urban Heat Island（ UHI） effect. The conditions in surrounding rural areas also affect the magnitude of UHI. UHI intensity was inversely correlated with rural Land Surface Temperature（ LST）. However

simply comparing the difference in LST between urban land and the surrounding rural area is not an effective method to quantify the intensity of UHI. Changes in urban construction land also varied in the rural area. Hence

the problem can be transformed into determining how areas affected by the UHI can be identified spatially.This paper researched the UHI effect during the period between 2001 and 2012 in the Beijing metropolitan area based on MODIS LST products obtained by using split-window algorithm. This paper presented the concepts of UHI footprint and capacity to spatially distinguish the areas affected by UHI. Then

the relationship between land use and UHI footprint was analyzed by using the radius method

and the influence mechanism of land use on UHI was discussed.UHI footprint and capacity differ significantly during daytime and nighttime. The area of urban island footprint in the daytime is 1. 5 times that in the nighttime in 2012. This finding is due to the comprehensive factor of differences in thermal characteristics of urban land and human activities. The high temperature zone spatially extended to the north and south during 2001—2012

and UHI footprint and capacity exhibited a periodical growth. The largest UHI footprint appeared in daytime in 2010

that is

the radius was 28 km

and the area of the UHI footprint was 2. 4 times that in 2001. UHI capacity is affected by the distribution and planning of urban green space and water function zone

even if UHI footprints are not different in two periods. The contributions of urban land and rural residential to UHI are significantly higher than the contributions of other land use types. When the area of construction land is more than 50%

the region produces obvious UHI.This paper presented improvement measures according to the spatiotemporal character of UHI footprint and capacity. Construction scale on the underlying surface is the critical mechanism of the urban thermal environment. This study can serve as a guide to plan and manage the urban thermal environment in cities

and it can help to control UHI effectively.