Abstract: Due to poor nutrients and low microbial activity,the gangue stockpile in the mining area is difficult to be reclaimed. Microbial remediation technology has become a research hotspot of ecological reclamation in the mining area. In order to clarify the reclamation effect of Trichoderma harzianum(TH),Bacillus mucilaginosus(BM) and arbuscular mycorrhizal fungi(AMF) in coal gangue stockpile with different particle sizes,eight treatment schemes were set up,including three single bacteria treatments, three Mixed treatments of bimicrobial agents, one mixed treatment of three bacteria and control treatment. The pot experiment was carried out to determine the growth index,matrix nutrient content and matrix microbial index of alfalfa. The results showed that in three single bacteria treatments,the AMF had the best comprehensive improvement effect on different particle size substrates. In general,the AMF could significantly improve the growth index and nutrient content of alfalfa,and the biomass of alfalfa was increased by 17. 39%-40.43%. The comprehensive improvement effect of mixed treatments of bacteria on different particle size substrates was better than that of single bacteria treatment. Among them,the mixed application of TH and BM and the mixed application of TH and AMF showed a strong complementary effect on the improvement of matrix catalase,sucrase,available phosphorus and MBC. The BM and AMF showed a strengthening effect on the content of alkaline hydrolysis nitrogen, available phosphorus, available potassium, MBC, phosphatase and protease activity. The comprehensive improvement effect of each treatment on small particle size matrix was better than that on large and medium particle size matrix. The reason was that the smaller the particle size of the substrate,the larger the specific surface area,the more conducive to the growth of microorganisms. At the same time,the pores of small particle size matrix were small,and the time for small pores to preserve water was longer than that for large pores. Among all treatments, The TH+BM+AMF,AMF+TH and TH+BM were the best comprehensive improvement treatments in large,medium and small particle size substrates,respectively. The biomass of alfalfa was increased by 82.61%,86.69% and 126.39%,respectively. There was a synergistic effect on root length,biomass and matrix MBN content of alfalfa. In summary,the TH,BM and AMF mixed application technology can be used as a good reclamation technology in gangue stockpile. It is suggested that the corresponding mixed application of bacteria should be selected according to the particle size of coal gangue in gangue stockpile.