Affected by the 4.2 ka BP event, the major ancient civilizations in the world and most of the Neolithic cultures in China suddenly collapsed. However, the Luoyang Basin in the central China hosted the successful transition from Henan Longshan Culture to Erlitou Culture at similar to 4.2 ka BP, and the successful transition made the Chinese civilization the only one in the world that has not been interrupted. To explore the environmental conditions and human activities in the Luoyang Basin at similar to 4.2 ka BP, we analyzed pollen assemblages, magnetic susceptibility, and grain size of HZ-1 section, and reconstructed the histories of the environmental changes (vegetation/hydrology) and the human-activity intensity changes with a chronological support of 17 AMS C-14 dates. Our reconstruction shows that the climate was relatively dry and the Huizui wetland was under a shallow-watered condition from 4990 to 4330 cal a BP. Subsequently, the climate became rather wet and the wetland was under a relatively deep-watered condition from 4330 to 4155 a BP. Followed was a period from 4155 to 3995 cal a BP when climate became relatively dry again and the wetland returned to a shallow-watered condition. The disappearance of the Huizui wetland at similar to 3995 cal a BP was followed by a wet interval lasting from 3995 to similar to 3955 cal a BP when the contemporary loess was strongly weathered. And, the wet interval was then succeeded by a dry interval lasting from 3955 to 3890 cal a BP during which loess deposition dominated. Our reconstruction of human-activity intensity shows that the intensity was rather weak from 4990 to 4330 cal a BP and increased slightly from 4330 to 4155 cal a BP. The human-activity intensity increased significantly from 4155 to 3995 cal a BP and then decreased considerably from 3995 to 3890 cal a BP. Our examination from a large-scale perspective shows that the 4.2 ka BP event corresponded to a relatively long interval of weakened Asian Monsoon spanning from 4400 to 3950 cal a BP. But, the middle and lower reaches of the Yangtze River basin and the southern margin of the Loess Plateau including the Luoyang Basin seemed to have responded to the weakened Asian Monsoon quite differently. Specifically, the 4.2 ka BP eventrelated weakening of East Asian Summer Monsoon (EASM) occurred during the earlier portion (4400-4100 cal a BP) of the Asian Monsoon weakening period (4400-3950 cal a BP) in the middle and lower reaches of the Yangtze River basin, and it occurred during the later portion of (4200-3950 cal a BP) in the southern margin of the Loess Plateau. We propose here that the change in the coupling relationship between the east-west thermal gradient of Equatorial Pacific (associated with ENSO) and the strength of Western Pacific Subtropical High (WPSH) was the main mechanism for this contrast. In other words, the earlier portion (from 4400 to 4100 cal a BP) of the Asian Monsoon weakening period corresponded with an ENSO negative phase (i.e., La Nino stage), under which the precipitation was low in the middle and lower reaches of the Yangtze River basin and high in the middle and lower reaches of the Yellow River basin. In contrast, the late period (4200-3950 cal a BP) of the Asian Monsoon weakening period corresponded with an ENSO positive phase (i.e., El Nino stage), under which the precipitation was high in the middle and lower reaches of the Yangtze River basin and low in the middle and lower reaches of the Yellow River basin.