The species and quantity of undergrowth weeds of chestnut forest in the northern Yanshan Mountains were investigated. Based on the field survey data of 2017, 2018 and 2020, Levins niche index and Pianka niche overlap index were used to analyze the niche dynamics of major undergrowth weeds, resource utilization, and interspecific competition of chestnut forest. The results showed that:(1) There were 53 species (48 genera, 27 families), 47 species (43 genera, 24 families), and 44 species (41 genera, 24 families) in the understory weed community of chestnut in 2017, 2018 and 2020, respectively. Among them, there were 15 species of dominant weeds. (2) Among the 15 dominant weeds, Humulus scandensand Chenopodium glaucumL. occupied a wider ecological niche and had a higher degree of diversity in their use of environmental resources. The niche width of Commelina communis, Artemisia argyi, Setaria viridis, Rubia cordifolia, Ixeris polycephala, Chelidonium majus, Viola philippica, Chenopodium glaucum, Digitalis purpurea and Glycine soja. were increasing, and these species had increased resource availability. (3) In the weed community, the number of major species with niche overlap value less than 0.2 decreased significantly, and the interspecific competition was more complex. The main weed species gradually increased their ability to make full use of the surrounding resources and environment. Accurate knowledge of weed occurrence, dominant population and community composition in Chestnut orchard can provide theoretical basis for targeted weed control in chestnut understory in northern Yanshan.