ObjectiveTo explore the differences of cognitive function in patients with treatment-resistant depression and drug-naive first-episode major depressive disorder， and to examine the relationship between severity of clinical symptoms and cognitive function， so as to provide references for prognosis improvement. MethodsFrom November 2016 to December 2019， 119 patients with drug-naive first-episode major depressive disorder and 82 patients with treatment-resistant depression in a hospital in Guangzhou were enrolled， meantime， another 71 healthy individuals recruited from the community were set as healthy control group. Clinical symptoms were assessed using Hamilton Depression Scale-17 item （HAMD-17） and Hamilton Anxiety Scale （HAMA）. Cognitive domains， including speed of processing， working memory， verbal learning and memory， and visual learning and memory were measured with the MATRICS Consensus Cognitive Battery （MCCB）. Multiple covariance analysis was used to compare the differences in cognitive function among three groups. Thereafter， partial correlation analysis was performed within patient groups to explore the relationship of HAMD-17/HAMA score with the four dimensions of MCCB. ResultsThe speed of processing， visual learning and memory scores of treatment-resistant depression group and drug-naive first-episode depression group were lower than those of healthy control group， and the working memory score of the treatment-resistant depression group was lower than that of the healthy control group， with statistical significance （P<0.05 or 0.01）. The speed of processing， visual learning and memory scores of treatment-resistant depression group were significantly lower than those of drug-naive first-episode depression group （P<0.05 or 0.01）. Partial correlation analysis within patient groups found that HAMD-17/HAMA total score had no correlation with the four dimensions of MCCB （P>0.05）. ConclusionCompared with drug-naive first-episode major depressive disorder patients and healthy controls， the impairments of speed of processing， visual learning and memory are more severe in patients with treatment-resistant depression. Moreover， the cognitive function impairment in patients with drug-naive first-episode major depressive disorder and treatment-resistant depression has no correlation with the severity of depressive and anxious symptoms.