Purpose. To study the species composition and the ratio of seed stocks in the soil of different biological groups of weeds in the agrophytocenosis of winter pea, and their influence on the yield formation depending on the sowing rate of the crop. Methods. Quantitative and weighting, agrochemical, analytical, and statistical methods were used. Results. Weeds that formed a significant seed stock, belonged to the families Chenopodiaceae (58%), Amaranthaceae (18%), Poaceae (9–11%), Brassicaceae (6%), Роlygonaceae (4.5–5.8%), and Asteraceae (1.5–2.2%). A significant raw and dry biomass was formed by Cirsium arvense (52 and 24 g/m2, respectively), Polygonum scabrum (46 and 22 g/m2), Thlaspi arvense (34 and 12 g/m2), Chenopodium album (34 and 14 g/m2), Polygonum convolvulus (27 and 13 g/m2), Sonchus arvensis (23 and 11 g/m2), Amaranthus retroflexus (21 and 10 g/m2), Ambrosia artemisiofolia (22 and 11 g/m2), Solanum nigrum (21 and 9 g/m2), Galium aparine (19 and 8 g/m2), Sinapis arvensis (18 and 8 g/m2), Setaria pumila, and Setaria viridis (9 and 4 g/m2). Conclusions. Changes in the productivity of winter pea at different degrees of weed infestation of the sowings were revealed. A significant influence of segetal vegetation on the crop yield was established at the pea seed sowing rate of 0.6 million seeds/ha, where the yield of the varieties ‘Enduro’ and ‘NS Moroz’ was only 3.01 and 3.13 t/ha, respectively. The density of segetal vegetation at the standard sowing rate of 1.1 million seeds/h and increased rate to 1.6 million seeds/ha did not affect the yield (3.33 and 3.34 t/ha, respectively). On thinned crops, weed infestation increases, which can affect the crop yield, as it has significant advantages for growth and competition with winter pea plants.