Cotton (Gossypium hirustum L.) as well as other crops are asking for an effective production with cost reduction and environment stewardship globally, especially in the developing countries. A new cotton planting strategy should be possible by shortening the growth season (less than six months rather than seven to eight months by late sowing and early harvesting) with low nitrogen (N) and high density. Therefore, a two-year (2018–2019) field experiment was conducted with a split plot design, two planting densities (D1, 6 plants m⁻²; D2, 8 plants m⁻²) as the main plot and three N rates (150, 180 and 210 kg ha^-1 referred as N1, N2, and N3, respectively) as the subplot, to determine the effects of planting density and N rate on cotton yield and biomass accumulation. Results showed that, averaged across years, cotton yield was greater for treatment D2 as compared with that in D1, and N3 did not differ from that in N2 but was greater than that in N1. The highest lint yield (1271.2 kg ha^-1) was achieved in D2N2 which no differ from that in D2N3 and D1N3. The maximal biomass (K) was achieved in treatment D2N2 (1032.4 g m⁻²) with the average speed (V_T) of 21.2 g m⁻² d^-1 during the fast accumulation period, and the maximal growth rate (R_m, 20.5 g m⁻² d^-1) of sink during the cotton growth and development. Seedcotton yield was positively correlated (r = 0.72) to the plant biomass during flowering and boll-setting period, and the yield was contributed directly by sink with a coefficient as high as 0.70, while it was contributed indirectly by flow and source with coefficients of 0.63 and 0.59, respectively. The results suggest that N reduction is feasible due to a quicker bulk sink biomass accumulation under a higher planting density, which benefits efficient cotton production in the Yangtze River Valley, China, and areas with similar ecology.