Objective　To examine the interrelation between the cognitive deviation and loneli-ness levels of medical students and its influencing factors. Methods　Totally 220 medical students in grade two of one medical school were selected by method of cluster random sampling. The data of the research were obtained through cognitive bias questionnaire（CBQ） and emotional-social loneliness questionnaire. Interrelation between the cognitive deviation type and condition of emotional-social lone-liness of medical students were analyzed by Pearson product-moment correlation two-tailed test. Multi-ple stepwise regression analysis was conducted by taking score of emotional-social loneliness as de-pendent variable and score of CBQ as independent variable. Differences in cognitive deviation and loneliness levels between rural and urban students as well as between students from single child family and students from non single child family were analyzed by independent-sample t test. Results　Neg-ative cognitive deviation of depression-distortion type was positively correlated with medical students' emotional isolation（r=0.161， P=0.021），social isolation（r=0.266，P=0.000）， emotional loneliness（r=0.340， P=0.000） and social loneliness （r=0.385， P=0.000）. The regression equation was： score of emotional-social loneliness=27.165+1.908（depression-distortion）+0.836（depression-non distortion）. Students from non single child family had higher scores than students from single child family in the perspectives of depression-distortion”（P=0.017）， social isolation（P=0.001）， emotional loneliness（P=0.016）， social loneliness（P=0.000）. Rural students had higher scores in the above four perspectives than urban students（P<0.05）. Conclusions　Negative cognitive deviation levels of medical students is positively correlated with emotion and social isolation conditions and loneliness experiences. Regres-sion analysis shows that unhealthy cognitive disposition and thinking mode probably are one of the im-portant reasons leading to medical students' stress disorder. Students from single child family and rural area may experience social loneliness more deeply and students from single child family have obvious cognitive deviation.