This invention relates to the field of microbial fermentation technology, specifically a method for preparing Rehmannia glutinosa through simultaneous fermentation with compound bacteria and a laxative effect. This method involves extracting four types of probiotics that meet national safety standards: Lactobacillus acidophilus, Bifidobacterium longum, Lactobacillus casei, and Saccharomyces cerevisiae, and then formulating a high-concentration compound bacterial agent according to the live bacteria ratio. The initial fermentation material is adjusted to a material-to-water ratio of 1:5 and a suitable pH is maintained. After autoclaving, the materials are inoculated with bacteria at a weight-to-volume ratio for biological culture. The entire system is placed in a 37°C environment for continuous constant-temperature static co-fermentation. Through specific enzymatic hydrolysis and metabolic pathways of multidimensional bacterial communities, the absolute content of the core active ingredientcatalpol and soluble dietary fiber in the final product is significantly increased. This bio-fermentation process effectively eliminates the potential risk of spleen and stomachirritation and damage from traditional Chinese medicinal materials. The resulting dry powderraw material can be widely and safely used in the preparation of microecological functional foods or pharmaceutical preparations targeting constipation symptoms caused by intestinal dryness and fluid deficiency.