In recent years, climate change is very likely to cause late sowing of Winter Wheat in China, affecting the growth quality of wheat seedlings. In order to study the problem of poor quality of wheat seedlings caused by late sowing, a randomized complete block experiment on the sowing date and cultivation regulation of winter wheat was carried out in Beijing from 2019 to 2021. Four sowing dates were set, from September 25 to October 25, and sown every 10 days as different accumulated temperatures before winter. Film mulching and supplemental application of N-fertilizer were used as late sowing control measures. To study the responses of population quality, individual traits and stems and tillers growth of winter wheat seedlings to accumulated temperature before winter and control measures. The results showed that the delay of sowing date (the decrease of accumulated temperature before winter) was not conducive to the formation of wheat population and individual quality before winter, and the total number of stems, tillers per plant, leaf area index, dry matter weight and nitrogen accumulation were gradually decreased. Among them, the leaf area index, dry matter weight and nitrogen accumulation have an exponential function relationship with the accumulated temperature before winter, that is, it decreases significantly with the decrease of the accumulated temperature before winter. The soluble sugar content and nitrate reductase activity in seedlings increased first and then decreased with the delay of sowing date. The accumulated temperature (t ≥ 0 ℃) decreased by 204.0 ℃, 148.0 ℃ and 134.4 ℃ on average every 10 days of sowing delay. The accumulated temperature before winter of the first and second sowing dates exceeds 550 ℃, and wheat seedlings can grow with high quality. The accumulated temperature of the third and fourth sowing dates decreased by 148.0 ℃ and 282.4 ℃ respectively compared with the second sowing date, and the growth quality of wheat seedlings was poor. Film mulching to increase the temperature could increase the total population number of wheat seedling stems by 42.9% and 148.4% at the third and fourth sowing dates. The number of individual tillers increased by 1.6 and 2.0 respectively. Increase the soluble sugar content in stems and leaves, tillering node, roots and the ratio of IAA/ZR in leaves. Supplementary application of nitrogen fertilizer had no significant regulatory effects on population quality, individual traits and stems, and tillers growth of late-sown wheat before winter. Based on the population quality and individual traits of wheat seedlings, under the second sowing date (October 5), the accumulated temperature before winter is conducive to the formation of high-quality seedlings. The daily average temperature is 15-17 ℃, which is the best sowing date of winter wheat in Beijing. Under the condition of late sowing, film mulching can effectively improve the overall quality of wheat populations and individuals before winter, and further promote the growth of seedling stems and tillers.