High-accuracy continuous measurements of atmospheric concentrations of CO2 were made from May 2016 to December 2017 using the Picarro G2301 analyzer at Xinglong station (40°24′N, 117°30′E, 940 MSL), 150 km northeast of Beijing. The near-ground CO2 measurements were calibrated by standards based on WMO procedures. The regional background measurements were filtered by the robust extraction of baseline signal method to study the seasonal and diurnal cycles. The regional background CO2 concentrations were low in summer. The maximum difference between the local sources and regional background CO2 concentrations occurred in summer and autumn, indicating a strong influence from local sources. Cluster analysis and potential source contribution function analysis showed that the long-distance transport of anthropogenic emissions in the Beijing–Tianjin–Hebei metropolitan area influenced the CO2 concentrations in Xinglong, especially in summer. The diurnal variation of CO2 was mainly influenced by the various vertical transport conditions of the tropospheric atmosphere in a day.