In order to study the tolerance mechanism of spring bread cultivars to wild oat competition, an experiment was conducted in research farm of Ramin Agricultural and Natural Resources University of Khouzestan as strip block with three replications during 2010-2011 growing season. Experimental factors were wild oat densities includ 0 (as control) and 80 plant/m2 as horizontal plots and ten wheat cultivars include Chamran (Atila), Baz, Atrak, Arvand, Maroon, Shoeleh, Chenab, Veree/Nak and Falat (Seri 82) as vertical plots. By using competition index, cultivars divided in four groups of mid-susceptible, medium, mid-tolerant and tolerant. Also modeling of competition of wheat cultivars with wild oat, between measured traits, trait of weed biomass has highest direct reduction effect (-0.609) on competition index. Also, wheat traits such as grain number in spikelet has highest direct reduction effect (0.498) and death plant percent has highest indirect reduction effect (-0.307) on competition effect. But wheat biomass although indirect increase effect by effect on weed biomass and thousand grains weight of wheat, has highest direct and positive effect (-0.395) on competition index. Other effective trait was thousand grain weight of wheat that by direct and positive effect (0.270) resulted in increase in competition effect of cultivars.