The invention relates to a straw-decomposition composite microbial preparation and a preparation method thereof. The straw-decomposition composite microbial preparation disclosed by the invention is prepared by mixing bacillus weihenstephanensis, bacillus amyloliquefaciens, bacillus megaterium, staphylococci, achromobacter xylosoxidans and aspergillus niger according to certain mass percent, is suitable for directly returning all rice straws to the field, can outstandingly accelerate the decomposition speed of straws, is favorable to transferring the transplanting stubble, can increase the organic content, enhance the soil enzyme activity, improve the soil physicochemical property and enhance the rice yield in a next season, and can also improve the soil, enhance the water and fertilizer utilization ratio, reduce the fertilizer, increase the efficiency, reduce the pollution of straw incineration on the environment and achieve the outstanding integrated benefit.