Abstract: Wanza40，a popularized hybrid in upland cotton，was used to study the performance and genetic models of heterosis of yield and fiber quality traits. The performance of yield in P1, P2, BC1, BC2, F1 and F2 populations was tested at four experimental environments，and the performance of yield in P1, F1, P2 and F2∶3 populations was further tested at two sites. Fiber samples of P1, P2, BC1, BC2, F1, F2 and F2∶3 populations were selected for examining fiber quality. The averaged heterosis, measured as departure from mid-parent value, for lint yield, seed cotton yield, boll number, boll size and lint percent in F1 were about 26.1％，23.7％，15.1％，6.6％ and 2.0％, respectively, and in F2 generation were about 21.1％，19.2％，13.0％，6.4％ and 1.5％, respectively. The heterosis for fiber quality was very small. The higher heterosis in F2 generation is very useful for cotton production. The result of genetic analysis, by segregation analysis on the major-polygene mixed inheritance model of quantitative traits from multi-generation and by weighted least square estimates method on the genetic model of additive, dominance and epistasis, indicated that dominance was the main genetic basis of heterosis of lint yield，pre-frost seed cotton yield, boll number, and lint percent. In general, there really existed genetic effects of major gene in yield and fiber quality of upland cotton.

Key words: Upland cotton, Heterosis, Major-polygene mixed inheritance model of quantitative traits, Genetic effects