Few empirical studies have examined the effects of individual difference variables (e.g., personality traits) and social environment variables (e.g., family environment) on adolescents’ moral judgment competence systematically. Based on the latest theories of moral judgment, this study tested the relationship of personality traits, family environment and moral judgment competence among middle school students. The aim is to provide some help for students’ moral psychological education and counseling. The participants were 900 students ranging from grade 1 of jurnior high school to grade 3 of senior high school. They are come from six urban districts and rural districts. 887 students finished the questionnaires (855 were valid, 96.4% ) which included three scales: Qingnian Zhongguo Personality Scale (QZPS), Family Environment Scale-Chinese Version (FES-CV, 3rd ed.) and Chinese Adolescent Moral Judgment Competence Test. In order to construct a relevant model for the different three variables, the statistical methods adopted correlation analysis, regression analysis and path analysis respectively. The research constructed four structural equation models: one direct effect model and three intervening process variable models. The models revealed that the personality traits and family environment variables to the middle students’ moral judgment have both directly effects and indirectly effects with relatively comprehensive. The results showed that the directly effects of personality traits factors influenting moral judgment competence are Good-heartedness and behavior style personality dimensions. Personality traits and family’s success, knowledge and control factors effect each other. And personality extroversion, behavior styles, good-heartedness, talent, emotionality and honesty indirectly influented it throught family achievement orientation, intellectal-cultural orientation and control. Furthermore, family’s success and control directly influented moral judgment competence. Family cohesion, achievement orientation, intellectal-cultural orientation, active-recreational orientation, moral-religious emphasis, organization and control indirectly influented it throught personality good-heartedness, talent and honesty. The findings revealed that the direct effects of middle school student’s personality traits, family environment on the moral judgment competence have more significance than the indect effects. Personality traits are the protective factors