Abstract: The results indicated that the two tested strains spr 45 and spr 29 could resist certain level of Mo.Ammonium molybdate was more suitable in combination with rhizobia than the natrium molybdate.Different strains had different Mo tolerance.The combined inoculant using ammonium molybdate had more viable rhizobial number than that of using natrium molybdate.The pH value of the combined inoculant rose along with the increase of molybdate concentration,also with prolongation of incubation time.Combining inoculant with natrium molybdate increased pH more significantly than that of using ammonium molybdate.Within 180 day incubation,the pH value and viable number of the combined inoculant with ammonium molybdate measured up the quality requirement of 'Rhizobial Fertilizer Standard'.Natrium molybdate was not suitable to be added into rhizobial inoculant,because of the low viable number and its high effect on pH(value).The pot experiment indicated that different strains symbiotic nitrogen fixation efficiency and the ammonium molybdate concentration were related.Spr 45 symbiotic N fixation efficiency was the best with ammonium molybdabte being 0.2% and the yield increased by 73.4%,13.7% compared with CK and traditional inoculant,respectively,nodule(occupancy) was 59.7%.Spr 29 was more effective when the concentration of ammonium molybdate was 0.3%.The(yield)(increased) by 73.4%,13.7% compared with CK and traditional inoculant,respectively,and nodule occupancy was 70.3%.Both of yield effects reached the significant level.