Loneliness refers to a subjective feeling of isolation, accompanying the perception that one’s social needs are not being met by the quantity or the quality of one’s social relationships. Loneliness has become one of the most common mental health problems and has a range of negative impacts on individuals. In order to suppress the adverse effects of loneliness, it was important and urgent to investigate its potential causes. Prior studies focused mainly on negative events happened in childhood on loneliness, and their results showed that childhood maltreatment and loneliness in adulthood had a direct association. And previous literature had documented the important influence of both cognitive factors and personality factors on the relationship between childhood maltreatment and adults’ loneliness. However, our knowledge of the specific underlying mechanisms of how childhood maltreatment affected loneliness in adulthood was fairly limited. In order to address this research gap, the current study examined the relationship between childhood maltreatment and loneliness in adulthood. Specifically, drawing from response styles theory and attachment theory, we constructed a mediation model that childhood maltreatment affected loneliness in adulthood via cognitive (rumination) and personality (core self-evaluation) factors. We further investigated the chain mediating roles of both core self-evaluation and rumination in the model. Participants (M = 19.54, SD = 1.86) were 811 college students recruited randomly from four universities. All of them completed four questionnaires: Childhood Trauma Questionnaire, Ruminative Responses Scale, Core Self-Evaluations Scale and UCLA Loneliness Scale. This study used AMOS 22.0 to analyze data collected by questionnaire survey. First, we examined the common method deviation analysis and used AMOS 22.0 to examine the measurement model. Then, we used the structural equation model and the bootstrap estimation procedure to analyze the mediating roles of both core self-evaluation and rumination between childhood maltreatment and loneliness in adulthood. Last, multi-group analysis was used to examine whether the structural model was stable when considering gender differences. The proposed structural equation model was tested and the results were as followings: (1) childhood maltreatment could affect loneliness in adulthood through the mediating role of rumination. (2) core self-evaluation fully mediated the association between childhood maltreatment and loneliness in adulthood. (3) childhood maltreatment could affect rumination through core self-evaluation, and then affected loneliness. That’s, core self-evaluation and rumination played chain intermediary roles. In addition, we further used the Critical Ratios of Differences (CRD) between the two models as an indicator to investigate the differences between male and female standard deviations. The results showed that there was no significant difference in the structural path of all variables. Therefore, the model in present study had cross-gender stability. This study indicated the underlying mechanisms of childhood maltreatment on loneliness in adulthood, including the indirect influence through rumination and core self-evaluation. And the present study was the first to demonstrate the chain mediating roles of rumination and core self-evaluation in the effect of childhood maltreatment on loneliness in adulthood. Therefore, the current study provided empirical evidence that childhood maltreatment was a non-negligible harm for loneliness in adulthood. And it extended related theories on suppressing the negative effects of early abuse. Our findings also deepen our understanding of the loneliness mechanism by examining the mediating roles of rumination and core self-evaluation under theoretical frameworks.