To study the effects of intercropping forage grasses on the composition and diversity of weed communities in an apple orchard in Nyingchi, Tibet, Two annual grasses (Avena sativa L. and Vicia sativa L.) and two perennial grasses (Medicago sativa L. and Dactylis glomerata L.) were single sown or mixed sown, with grasses natural growing after clear tillage as a control, and then the weed communities were surveyed in 2011 and 2022, respectively. A total of 33 weed species in 31 genera and 17 families of were found in the experimental plots in the studied two years, the dominant families were Gramineae, Leguminosae, Polygonaceae, and Asteraceae, and the dominant species were Eragrostis pilosa (L.) Beauv., Eragrostis pilosa (L.) Beauv., Galinsoga parviflora Cav., Taraxacum mongolicum Hand.-Mazz, and Persicaria microcephala (D. Don) H. Gross. Intercropping forage grasses reduced weed species richness and decreased the importance values of the dominant weed species, which were dependent on forage grasses species and plant year. Intercropping forage grasses also reduced species diversity of weed communities, both planting year and cropping pattern significantly affected the community diversity and dominance. The weed control efficacy of Gramineae forage was better than that of Leguminosae forage, and the mixed sowingwas better than that of single sowing treatment. The study indicated that planting forage grasses should consider their growth period, annual forage has better weed control effect in short period, while perennial forage is suitable for long-term grass planting in the orchard.