In this research, calcareous purple soil deficient in Fe was used for potexperiment. Three strains of Bradyrhizobium Spr3-5, Spr3-7, Spr4-5 and gusA-and celB-labeled strains gusA 3-5, gusA 3-7, gusA 4-5, celB 3-5, celB3-7, celB 4-5 were selected inoculate T ianFu 9 peanut. Root nodule formed by gene marker strains would have color reaction with the test reagent. This characteristic can be used to detect effect of Fe fertilization and its application rate on effectiveness and competitiveness of the peanut Bradyrhizobium symbiosis. Results show that in calcareous purple soil deficient in available Fe, spraying of FeSO₄·7H₂O solution, inoculation of Bradyrhizobium or combination of the two could all promote symbiotic nitrogen fixtion and competitive ability of peanut Bradyrhizobium in nodulation, but the effect was the best with the combination, followed by inoculation and then Fe application. The effect of spraying 0.2% FeSO₄·7H₂O solution was much better than that of spraying 0.3% FeSO₄·7H₂O solution. Plant total nitrogen content and total chlorophyll content, which are both important indices of sym biotic nitrogen fixation, showed extremely significant correlations with peanut yields, with correlation coefficient being 0.763 and 0.795, respectively. Results of the test with either gusA or celB labeled strains were almost the same. The nodulation rate of the three labeled Bradyrhizobium strains, Spr3-7, Spr4-5 and Spr3-5 was averaged to be 79.46%, 75.62% and 74.41%, respectively. Interms of effectiveness and competitiveness, Strain Spr4-5 took the lead and was followed by Spr3-7 and Sp3-5 in the end.