In order to clarify the impact of nitrogen application rate on cotton growth and yield in summer direct seeding cotton in the Yangtze River Basin，providing scientific basis for evaluating the effect of nitrogen fertilizer application and improving economic benefits，a randomized block design was adopted in the field experiment for two consecutive years，using 425 varieties from China Cotton Institute as materials. Six nitrogen application rates were set up，i.e. 0，60，120，180，240，and 300 kg/hm²，and were marked as N0，N1，N2，N3，N4 and N5，respectively. The changes in cotton agronomic traits，biomass，leaf area index(LAI)，leaf nitrogen content，seed cotton yield，and other indicators with nitrogen application rate were analyzed. The comprehensive evaluation of nitrogen application effects was conducted using factor analysis，principal component analysis，and membership function analysis to simulate the optimal economic nitrogen application rate. The results showed that nitrogen application promoted the growth of cotton，and significantly increased the LAI，leaf nitrogen content and population biomass. Compared with 240 kg/hm² nitrogen application treatment，300 kg/hm² nitrogen application had no significant effect on agronomic traits，LAI and dry matter weight of reproductive organs per plant. The number of bolls per plant，weight per boll，and seed cotton yield of cotton increased with the increase of nitrogen application，while the lint percentage slightly decreased. The seed cotton yield of 300 kg/hm² nitrogen treatment was significantly higher than those of 0-120 kg/hm² nitrogen treatments，but it was not significantly different from that of 180 and 240 kg/hm² nitrogen treatment，and even significantly lower than that of 240 kg/hm² nitrogen treatment by 9.46%. The membership function score was the highest for a nitrogen application rate of 240 kg/hm²，and the optimal economic nitrogen application rate for a comprehensive two-year simulation was 250.91 kg/hm². Therefore，the fertilization effect of 240 kg/hm² of nitrogen on summer direct seeding cotton in the Yangtze River Basin was the best，saving 20% of nitrogen fertilizer compared to 300 kg/hm² of nitrogen，and increasing seed cotton yield by 74.98 kg/hm². The recommended optimal economic nitrogen application rate for this mode was 250.91 kg/hm².