Objective To analyze the cognitive function of first episode schizophrenia, bipolar disorder and depressive disorder. Methods 60 cases of patients with first episode schizophrenia, 55 patients with bipolar disorder were divided into manic subgroup (35 cases) and depression subgroup (20 cases), 40 patients with depressive disorder, which were selected in our hospital from October 2014 to October 2016, 60 normal subjects were selected as the control group. RBANS (neuropsychological test system) was used to evaluate the cognitive function. Results The total scores of RNANS in the first episode schizophrenia group and bipolar disorder group were significantly lower than those in the control group (P<0.05). The scores of immediate memory factor in patients with schizophrenia, bipolar disorder and depressive disorder were significantly lower than those in the control group , The scores of speech function factors in the first episode schizophrenia, bipolar disorder and depression group were significantly lower than those in the control group, and the score of speech function factor in the double obstruction group was significantly lower than that in the first episode schizophrenia group. The score of attention factor in schizophrenia group was significantly lower than that in depressive disorder group and control group. The score of delayed memory factor in patients with first episode schizophrenia, double obstruction and depressive disorder was significantly lower than that in control group, the difference was statistically significant (P<0.05). Conclusion The first generation of schizophrenia, bipolar disorder, depression, cognitive function in patients with varying degrees of injury, first episode schizophrenia is lighter than bipolar disorder, more severe than depression.