The invention provides a preparation method for a composite material capable of simultaneously repairing heavy metals and glyphosate. The preparation method comprises the following steps: mixing biochar with a culture solution, and carrying out sterilizing at a high temperature; then inoculating a seed solution, and carrying out shaking culture in a shaking bed so as to complete soaking fixation of the biochar to microbes; and mixing an obtained solution with a mixed solution of polyvinyl alcohol with a concentration of 10% and sodium alginate with a concentration of 2% in an equal volume, then dropwise adding an obtained bacteria solution into a calcium chloride solution of saturated boric acid with a concentration of 5% so as to obtain biochar fixed microbial balls, immersing the balls in glycerol, and carrying out freeze-thawing for a plurality of times so as to obtain a product. Compared with traditional graphene or active carbon materials, the biochar microbial composite materialprepared by using the preparation method provided by the invention can adsorb the heavy metals and the glyphosate, and can degrade the glyphosate at the same time; meanwhile, the preparation process of the material is simple and has low cost.