Abstract: Preparation technology of mixed fermentation for the production of propionic acid and explore the optimal process conditions were studied by using Propionibacterium acidipropionici CGMCC1.2225 and yeast.The optimum fermentation conditions by single-factor experiment and orthogonal experiment were determined:Saccharomyces cerevisiae as an auxiliary bacterium, inoculation ratio was Pa∶Sc=2.5∶1, the inoculation interval time was 8h, and temperature was 30℃, 2mol/L NaOH solution as neutralizing agent, the incubation time was 180h.Under the optimal conditions, the yield of propionic acid was 24.16g/L by using mixed fermentation technology, which increased 46.34% compared with the pure culture fermentation.