The amount of dry matter in winter rapeseed plants at different growth stages affects the seed yield. More dry matter accumulation from turning green to beginning-flower stage leads to higher seed yield. The number of pods is related to dry matter accumulation at different stages, with more pods linked to more dry matter. Seed number per pod is influenced by dry matter accumulation at specific stages. The weight of 1,000 seeds is only affected by dry matter accumulation after the ending-flower stage. Applying more nitrogen and delaying its application can increase dry matter accumulation and seed yield, with the best results seen when nitrogen is applied at budding and flowering stages.