The invention discloses a fermented soybean meal with anti-diarrhea function and preparation method of the fermented soybean meal. The fermented soybean meal comprises the following components in part by weight: 450-500 parts of non-transgenic soybean meal, 90-110 parts of microorganism strain materials, 300-350 parts of water and 20-30 parts of molasses. The preparation method comprises the following steps: uniformly mixing the non-transgenic soybean meal, the probiotic strain material and the molasses to perform solid fermentation by adopting the multi-strain mixed fermentation technology, controlling environment conditions such as temperature and material moisture in microorganism growth, metabolism and enzyme production process to guarantee the acid production and enzyme production capacity of the microorganism and the accumulation of enzyme preparation content in the fermentation process; and drying the material at low temperature after the fermentation is finished so that the prepared fermented soybean meal further contains a mass of nutrition substances such as amino acid and active probiotics besides a mass of organic acid, thereby degrading the soybean antigen, improving the digestion utilization rate of the fermented soybean, and effectively reducing the piglet diarrhea.