[ Objective] The study aimed to explore the function mechanism of microbial ecological agent DUAN-NAI-AN on controlling weaned piglet diarrhea. E Method] DUAN-NAI-AN was given to the weaned piglets by oral administration and its effects on diarrhea rate, growth performance, in- testinal microflora, pH values of different parts of the intestine and intestinal mucosal morphology were observed. [ Result] DUAN-NAI-AN could im- prove the growth performance of weaned piglets by increasing the growth rate and phase weight gain, showing as higher livability, average daily gain and daily feed intake as well as lower diarrhea rate with 19.24% decline by contrast to the control. In addition, DUAN-NAI-AN could keep the intestinal mucosal mechanical barrier and normal digestive function by strengthening intestinal resistance and thus enhance the intestinal mucosal im- mune level. It could also decrease the proportion of potential pathogens and their toxicity effects inside the intestine to help the piglets transfer to and then maintain the dynamic balance of intestinal microflora in a very short period, and it also showed a trend of decreasing the pH value of piglet in- testinal contents. [ Conclusion] DUAN-NAI-AN is an effective microbial ecological agent for the control of weaned piglet diarrhea.