The invention discloses a composite microbial culture starter and a preparation method thereof, and aims to solve the technical problem of efficient and comprehensive organic waste fermentation and composting processing. The composite microbial culture starter comprises a carrier and a compound strain, the carrier is natural zeolite powder, and the compound strain comprises bacillus subtilis, lactobacillus acidophilus, lactobacillus delbrueckii subspecies bulgaricus, saccharomyces cerevisiae, bacillus megatherium and clostridium pasteurianum. The preparation method includes inoculation, primary culture, secondary culture, mixing to obtain a compound bacterium fluid, adsorption of the compound microbial into the natural zeolite powder with the granularity of 200 mesh, and drying to obtain the composite microbial culture starter. Compared with the prior art, by efficient and comprehensive of the decompose organic wastes, the pollution caused by the organic wastes on the environment can be completely solved by the composite microbial culture starter, the resource properties of the organic wastes are improved, and the prepared multifunctional organic fertilizer provides comprehensive nutrients needed for plant growth, and improves the soil very well.