The invention provides a bacillus fermentation medium for efficiently producing short branched fatty acid by waste cakes and bean dreg resources and a fermentation process. Efficient production of theshort branched fatty acid is achieved by matching specific medium compositions with culture conditions. A fermentation medium formula comprises, 10-100g / L of corn starch, 20-100g / L of waste organic nitrogen sources, 1-10g / L of ammonia chloride, 3-15g / L of calcium carbonate, 1-10g / L of dipotassium phosphate, 1-10g / L of magnesium sulfate, 0.005-0.10g / L of manganese sulfate and pH (potential of hydrogen) is 6-8. Fermentation culture conditions include that culture temperature is 25-40 DEG C, the rotating speed of a shaking table is 180-240r / min, and fermentation time is 30-60 hours. According tothe fermentation medium, low-cost soybean residue, rape seed cakes and cottonseed cakes serve as fermentation raw materials. Under the process conditions, the yield of the short branched fatty acid is increased by fermentation verification of geobacillus, bacillus subtilis and bacillus amyloliquefaciens. The process has the advantages that the process is simple in assembly, environmentally friendly, economical, high in yield, stable and wide in applicable range. The fermentation medium has a certain application prospect.