The invention provides a method for detecting food-borne pathogenic bacteria in a microecological active bacterial preparation through multiplex PCR. For the method provided by the invention, the multiplex PCR technology is mainly adopted, and the method adopts the PCR reaction in which multiple specific primers are added in the same reaction system, and multiple nucleic acid fragments are simultaneously amplified. According to the method, the specific primers of seven common food-borne pathogenic bacteria including salmonella, escherichia coli, bacillus pumilus, bacillus subtilis, staphylococcus aureus, pseudomonas aeruginosa and aspergillus niger are designed, seven target bands are simultaneously amplified in the same system, meanwhile, the specificity among each other is good, the limit of detection of the method achieves 200fg/[mu]l (template concentration), the corresponding concentration of bacterium is 120CFU/mL, the standard of the food safety can be achieved, the common pathogenic bacteria can cause the pathogenic effect when the concentration is 1000CFU/mL, therefore, the method is high in sensitivity, and is rapid, simple and convenient, and the cost is very low.