Abstract: Charcoal preserved in loess-soil profiles in the northern part of the Longdong Loess Plateau has recorded the fire history and landscape evolution connected with climatic variations and human activities.The profile is situated on the isolated flat-topped Majiayuan loess hill over the Heshui Valley,on the slope of which situated the Jiuzhan Site of the Siwa Culture(3350-2650aB.P.).Archaeological investigations indicate that a large number of graves of the Siwa Culture distribute from the pediment to the upper slopes of the Majiayuan hill.Moreover,the remains of the Laoguantai Culture(8000-7000aB.P.)are also identified with the presence of the orange red and brown-colored pottery shards,as well as charcoal analysis in the same profile.In this research,samples were cautiously taken every 2cm down the profile.Field investigation and analyses of Total Organic Carbon(TOC),magnetic susceptibility,and charcoal analysis in this Holocene Loess profile in Heshui,Gansu Province have revealed the relationship among Holocene wildfire events,human activity,and climatic changes.The results show that before 11500aB.P.,the climate was arid and wildfire occurred frequently over semi-desert grassland.The frequency of wildfires was reduced during the early Holocene.During the Holocene climatic optimum between 8500aB.P.and 3100aB.P.,natural wildfires were rarely found.Pathogenic alteration to the accumulated dust processes were so active that forest-grassland formed under the humid warmer climate of the Holocene Mega Thermal.However,localized wildfires in connection with human activities frequently occurred.Fire seemed to be applied to vegetation clearance for land reclamation for millet cultivation in the early Neolithic Age(8000-7000aB.P.)During the Late Holocene(3100aB.P.-0),the wildfires events occurred less frequently and soils were deteriorated due to an abrupt climatic reduction and intensive human activities.Land-use was shifted from arable farming to nomadic in the upper and middle reaches of the Jinghe River drainage.After 1500aB.P.,the amount of charcoal sharply decreased and fire occurrence disappeared gradually because of the development of mixed agriculture of cultivation and semi-animal husbandry.The results indicate that under the circumstances of climatic variations,wildfires seemed to be not only one of the factors which interfered the ecological environment,but also a direct factor that caused great changes of ecological environment in the northern part of the Longdong Loess Plateau.With the widespread of human activities,wildfire events had already accelerated the transformation of the ecological environment of that time without being consciously noticed.Thus,it is of great importance for us now to study the interaction between wildfire occurrences and human activities and it is also worthwhile doing some scientific research into a variety of changes that may impact the ecological environment.