The invention relates to a microbial agent for promoting rootage, preventing continuous cropping and performing ecological restoration on soil for planting bananas and a preparation method thereof, and the microbial agent is prepared by inoculating a production strain into a sterile culture medium containing a carbon source, a nitrogen source, an inorganic salt and water, performing aerobic fermentation under the conditions that the temperature is 30-37 DEG C and the pH value is 7.4-7.6, performing primary amplification culture respectively, mixing primary amplification culture solutions with equal mass, further performing secondary and tertiary amplification culture, finally adsorbing fermentation end products and immobilizing on a carrier for preparing the microbial agent, wherein the production strain is selected from bacillus subtilis, bacillus licheniformis, saccharomyces bayanus, paecilomyces lilacinus, streptomyces microflavus and bacillus polymyxa. The microbial agent can be used for effectively preventing dead seedlings, yellow seedlings, wilt, leaf spots, root rot and other soil ecological diseases during the planting process of the bananas, the production cost is low, the fermentation period is short, the flora density is high, and the microbial agent can be used for further promoting the growth of roots, loosening the soil, strengthening the seedlings, removing the pollution caused by residues of pesticides and fertilizers and playing a soil ecological restoration role.