Abstract: Objective To explore the influence of duration of untreated psychosis(DUP) on the cognitive functions and prognosis of drug-naive patients with first episode schizophrenia. Methods A total of sixty-eight drug-naive patients with first episode schizophrenia were randomly(by DUP) divided into short DUP group(n=33) and long DUP group(n=35).The WCST and P300 were used to evaluate the cognitive function at baseline,3rd month and 12th month after the treatment,and the results were contrasted with 35 health controls.ANOVA was used to analyze the data. Results ①Before the treatment,there were significantly differences in the cognitive function(P=0.000-0.006) between the DUP group and the control group;there was significantly difference in cognitive function(P=0.000-0.046) between short DUP group and long DUP group,except completing the number of classification and latency of P300(P=0.393,0.484).②After the treatment,there were still significantly differences in cognitive function between the long DUP group and control group(P=0.000-0.026),though the cognitive function of patients in the long DUP group was improved at some extent;However,there were significantly differences only in completing the number of classification and amplitude of P300 in short DUP group(P=0.042,0.000);③After the treatment,the cognitive function of the patients in short DUP was recovered obviously as compared with the patient in the long DUP,the differences by ANOVA was significant(F=4.258-6.764,P=0.017-0.045) except in completing the number of classification. Conclusion DUP had adverse effect on the cognitive functions of schizophrenia patients.To reduce the prevalence of long DUP should improve the recovery of the cognitive function of patients.