1300 county-level administrative units across China were considered for the study. County-level land usage data and socioeconomic data were used to calculate the total carbon sinks in China from 1990 to 2015. Combining standard deviation ellipse, spatial autocorrelation, cold-hot spot analysis, and geographic weighted regression analysis methods, the spatiotemporal differentiation characteristics and factors influencing these carbon sinks were explored. This study aims to provide a reference for optimizing China's land development patterns to implement differentiated emission reduction paths and promote the establishment of an ecological civilization. The research shows that: (1) In terms of spatiotemporal changes, China's carbon sinks showed a declining trend from 1990 to 2015, with a reduction in carbon from 133077900 tons to 131982700 tons. Forestland was the primary type of carbon sink, and the proportion of the remaining types were basically unchanged. In terms of spatial distribution, the carbon sinks were generally greater in the west than in the east, following a west > northeast > south > middle pattern. (2) During the research, the spatial distribution center of the carbon sinks was moving to the southwest, and the distribution range was shrinking. The influence of the southwest region on the overall spatial pattern of the carbon sinks was strengthened. From 1990 to 2015, the degree of cold and hot spot agglomeration of the carbon sinks showed a stable fluctuation. The spatial agglomeration showed clusters of high-value and low-value numbers, and sporadic distribution of high and low regions. (3) By analyzing influencing factors in 2015, economic development, industrial structure, and land usage, all demonstrated impacts on carbon sinks, indicating spatial heterogeneity. It is recommended to increase carbon sinks and reduce emissions at county-level by proper planning of land usage for non-construction land, formulating strategies for increasing carbon sinks and reducing emissions for various regions, and controlling the extent of land used for construction.