Objective: To understand relationship of positive and negative peer events with mental health problems among college students, so as to provide a scientific basis for improving mental health level of college students. Methods: A total of 1 640 freshmen to juniors were randomly selected from two universities in Anhui Province from October to November 2023 by a combination of convenience sampling and cluster random sampling method. The positive and negative peer events, self perceived loneliness and stress levels, anxiety and depression symptoms of students were investigated by using the questionnaire star online. Group comparisons were conducted by using analysis of variance and Chi square test, and multivariate binary Logistic regression and linear regression were used to analyze relationship of positive and negative peer events with mental health problems among college students. Results: About 35.4% of college students reported that they experienced at least one type of negative peer events, and 91.3% reported that they experienced at least one type of positive peer events. After controlling for covariates,multivariate regression analysis found that experiencing 1, ≥2 types of negative peer events were positively correlated with loneliness scores of college students ( β = 1.36,4.04), as well as an increased risk of anxiety symptoms ( OR =2.24,4.33) and depression symptoms ( OR =2.19,4.01); and experiencing ≥2 types of negative peer events was positively correlated with stress scores of college students ( β =1.12)( P <0.05). Experiencing 5-6 and 7 types of positive peer events were negatively correlated with loneliness scores of college students ( β = -1.79, -2.44) and stress ( β =-0.75, -1.12); and experiencing 7 types of positive peer events were associated with a lower risk of anxiety symptoms ( OR =0.74) and depressive symptoms ( OR =0.80) ( P <0.05). The number of negative peer events was positively correlated with loneliness scores ( β =0.80) and stress scores( β =0.24), as well as the risk of anxiety symptoms ( OR =1.30) and depressive symptoms ( OR =1.27) among college students ( P <0.05). The number of positive peer events involved was negatively correlated with loneliness scores( β =-0.39) and stress scores( β =-0.19), as well as the risk of anxiety ( OR =0.92) and depressive symptoms ( OR =0.93) among college students ( P <0.05). The analysis of the moderating effect found that in different groups of positive peer events, reporting 1, ≥2 negative peer events were positively correlated with loneliness scores of college students ( β=1.08- 4.96), as well as an increased risk of anxiety symptoms ( OR =1.79-6.20) and depression symptoms ( OR =1.78-6.77) ( P <0.05); and β and OR coefficients were highest in the group reporting 0-4 types of positive peer events, followed by the group reporting 5-6 types of positive peer events, with lowest coefficients in the group reporting 7 types of positive peer events. Conclusions Negative peer events are positively correlated with psychological problems in college students, and positive peer events are negatively correlated with mental health problems. Positive peer events could alleviate the impact of negative peer events on mental health problems.