To look for the toxicity fraction of Euphorbia pekinensis and discuss the vinegar processing mechanism. The level of intestinal edema, water content of intestine and stool, IC50 values of IEC-6 were applied to evaluate the toxicity of different fractions. RT-PCR was employed for detecting AQP1, AQP3 mRNA expression. The petroleum ether (PE) fraction and ethyl acetate (EtOAc) fraction could significant cause intestinal edema in mice, increase the water content of duodenum, colon and stool, inhibited the mRNA expression of AQP1 and increased the mRNA level of AQP3 in colon, and the petroleum ether (PE) fraction was more poisonous. After the petroleum ether (PE) fraction was processed with vinegar, the level of intestinal edema, water content of duodenum, colon, stool and inhibition ratio of cells line were reduced. And we compared the composition change after vinegar processing, finding that the conpekinensis.