In order to discuss the reasonable level of nitrogen application to direct seeding cotton after rapeseed harvest based on the concept of "increasing production without increasing investment" in the cotton area of the Yangtze River Basin, we selected the early-maturing cotton cultivar Huamian 3097, conduct a field experiment in 2022-2023, and six nitrogen rates (kg/hm2) treatment including 180 (N180), 210 (N210), 240 (N240), 270 (N270), 300 (N300), and 330 (N330). Field experiments to investigate the effects of nitrogen rates on cotton development, photosynthetic characteristics, and yield. The results showed that: cotton yield, N270 and N300 were comparable, but higher than N180 and N330.The average across two years seed cotton yield of N270 was 7.0% and 5.4% higher than that of N180 and N330, respectively, and its number of bolls per unit area was 24.9% and 21.6% higher than that of the two, and the differences in plant height, number of fruit branches, height of first fruit branches, number of green leaves, and number of stem nodes were similarly between treatments. Cotton canopy light transmittance, which decreased with growth stage, decreased with increasing N rates, within canopy height 30 - 50 cm and cotton row 20 cm, N270 was 23.9% greater than N330, 10.0% lower than N180, and comparable to N300. Net photosynthetic rate, transpiration rate and stomatal conductance, N270 (N300) is higher than N180 and N330; intercellular CO2 concentration, N270 is lower than N180 and N330. it can be seen that, wheat (rapeseed) after direct seeding cotton, nitrogen fertilizer in 270 kg/hm2, is conducive to the development of cotton growth and development, increase the number of bolls per unit area, improve the canopy light transmission conditions, improve the photosynthetic performance, and obtain a higher yield, so as to obtain higher yield.