Studies on alluvial pollen from 13 hydrological stations in different river flow periods（low river flow, flood, normal river flow）show that alluvial pollen assemblages are influenced by florescence changes of the plants growing in the Luan he River Basin Arboreal pollen percentage was higher than that of herb pollen during the low river flow period, which corresponded with the flowering period of most trees in spring Herb pollen percentage was higher than that of arboreal pollen during the normal river flow period, which corresponded with the flowering period of most herbs in late summer and autumn Herb pollen percentage was slightly higher than that of arboreal pollen during the flood period Arboreal pollen in alluvium mainly came from the surface pollen fallen on the ground in spring which was carried by sheet flow during the floodsAlluviums in Yanshan area are mainly formed by floodsTherefore, 20%～40% aboreal pollen of alluvial pollen assemblages during the floods represent 20%～25% of forest cover of Yanshan area This is a useful reference to reconstruct forest cover quantitatively