With the development of urbanization in China, construction land (CL) expansion is obvious, and urban heat island (UHI) is becoming more and more serious. Many scholars have shown a strong interest in the study of UHI caused by land expansion, but less attention has been paid to the coupling relationship between CL expansion and high-temperature area (HTA) expansion during the process of urbanization. This study obtained the land surface temperature (LST) data of China’s three major urban agglomerations (CTM-UAs) in 2000, 2005, 2010 and 2015. Then this paper used overall coupling model and spatial coupling model to reveal the coupling relationship between the CL expansion and HTA expansion of CTM-UAs in different periods. The results showed that: (1) From 2000 to 2015, the trend of CL expansion and HTA expansion in CTM-UAs was synchronous; (2) The distance between the CL barycentre and HTA barycentre in CTM-UAs was shrinking, the spatial overlap was constantly strengthening, and the overall coupling was constantly strengthening. And the highest value of the overall coupling was reached in 2015; (3) The number of grid units of very strong coupling and strong coupling increased with fluctuation in Beijing-Tianjin-Tangshan Urban Agglomeration (BTT), that in Yangtze River Delta Urban Agglomeration (YRD) was increasing, and that of Guangdong-Hong Kong-Macao Urban Agglomeration (GHM) has gone through the process of increasing to decrease.

The saturation of night light data caused by sensor defects conceals the differences and details of light luminance in the urban area, which greatly limits the application of Nighttime Light (NTL) in the study of urbanization. Although some methods have been proposed to mitigate the saturation of NTL data, the research of desaturation is worth further advancing due to its shortcomings in highlighting light differences and spatial resolution. Therefore, we propose a new spectral index, the Vector Data Adjusted NTL Index (VDANTLI) after analyzing the influence of different auxiliary parameters on saturation elimination. Then, we select the three most developed urban agglomerations in China and make a series of qualitative and quantitative analysis. The results of various assessments confirm that VDANTLI can effectively alleviate NTL saturation and enhance urban lighting differences. Moreover, by dynamically adjusting the length of the grid and single-phase vector data modified time-series NTL data, we further achieve the resolution-series and time-series VDANTLI. Therefore, compared with previous desaturation models, the VDANTLI can be used as an effective indicator and even an indispensable basic data for urbanization research and socio-economic spatial analysis because of its unique advantages in spatial resolution and the capability in time-series native NTL desaturation.