Abstract: 【Objective】 To construct the Bacillus compound flora, optimize the flora combination and study its herbicidal spectrum, crop safety and herbicidal activity against Avena fatua L., providing new ideas and theoretical basis for the development of new biological herbicides.【Method】 The Bacillus strains D30202, JZ1-1-9, JZ2-4-15 and JZ2-2-1 screened by the research group in the early stage were used as materials. The compatibility between the strains was determined by the in-dish confrontation test, and the growth curve of the strains was determined by spectrophotometry to determine the strains and combination periods for constructing the composite flora. The root length, bud length inhibition rate, dry weight and fresh weight inhibition rate of the compound flora on weed seed germination were determined by seed germination bag method to optimize the strain combination type. The pot experiment was used to evaluate the weed control spectrum and crop safety of the optimal combination flora. The malondialdehyde (MDA) content of crop leaves and the activities of three defense enzymes, superoxide dismutase(SOD), catalase(CAT) and peroxidase(POD), were measured as indicators of the response to the weed control activity of A. fatua L.【Result】 There was no antagonistic relationship between each two strains to be selected and the growth cycle was the same, and the compound flora 2-9-15 constructed by strains D30202, JZ1-1-9 and JZ2-4-15 was the optimal combination. The combined effect of the compound flora on seed germination and seedling growth of A. fatua L. was the most significant. The inhibition rates of root and shoot growth were 39.17% and 73.49%, respectively, and the inhibition rates of fresh and dry weight of seedlings were 25.11% and 21.26%. The herbicidal broad-spectrum and crop safety of the compound flora 2-9-15 in the pot experiment were higher than that of quizalofop-p-ethyl. Except for gramineous crop Hordeum vulgare, it had high safety to local crops such as Zea mays L., Chenopodium quinoa Willd., Trticum aestivum L., Vicia faba L., Pisum sativum L. and Solanum tuberosum L. After three-leaf stage A. fatua L. was sprayed with quizalofop-p-ethyl and compound flora for 3 d, the MDA content, SOD and CAT activity in leaves decreased and the decreasing trend was consistent.【Conclusion】 The compound flora 2-9-15 has high herb-inhibitory activity and broad-spectrum, and has the potential to be developed as a biocontrol agent for the control of gramineous weeds such as A. fatua L.