To investigate the copeptin in evaluating the severity and prognosis of acute organic phosphorus pesticide poisoning. Methods A total of 210 patients with acute organic phosphorus pesticide poisoning were selected from Gansu provincial hospital between Jan. 2011 and Dec. 2016. And they were divided into mild group, moderate group and severe group in accordance with their clinical symptom and the level of AChE. Besides, 70 cases of health people were selected as the control group. Copeptin was detected by ELISA; and APACHEⅡ score, myocardial enzymes, cTnI and some blood biochemistry indexes were detected in the two groups. Results The acute organic phosphorus pesticide poisoning groups′ copeptin content were more than control group, the difference was statistically significant(P＜0.05). As the poisoning degree increased, the content of copeptin and APACHEⅡscores increased(P＜0.05). Copeptin content and APACHEⅡscores in death group were higher than survive group(P＜0.05). For acute organic phosphorus pesticide poisoning patients, copeptin content had positive correlation with APACHEⅡ scores, CK-MB, LDH and cTnI(P＜0.05). Conclusion The blood copeptin can be an important indicator in evaluating the severity and prognosis of acute organic phosphorus pesticide poisoning.