With the rapid development of social economy and the increasingly fierce competition, college students which are lack of social experience and powerful self-adjustment ability have a higher risk of depression. The high incidence and harmfulness of depression make it an important research content of psychology, sociology and psychiatry to explore the influencing factors and mechanism of college students' depression. Some empirical studies have proved that negative life events are a risk factor for college students’ depression, but the mechanism (mediating and regulating effect) of negative life events on college students’ depression still needs further investigation. Studies have shown that when individuals are faced with negative life events, they are more likely to turn to the Internet to escape the frustration of life pressure and become addicted to the Internet, and Internet addiction is often significantly positively correlated with depression. The diathesis-stress model of depression suggests that individuals are more sensitive to stressful events in the environment because they carry certain vulnerability qualities, thus leading to depression. Therefore, we brought Internet addiction and 5-HTT1A gene rs749098 polymorphism into the currents and constructed a moderated mediator model to explore the mechanism of negative life events on college students’ depression. A total of 301 college students (74 boys and 227 girls) participated in this investigation. After given informed consents, they completed Center for Epidemiological Studies Depression Scale, Adolescent Self-rating Life Events Check List and The Chinese Version of the Internet Addiction Scale. Professional nurses extracted 2.5 ml venous blood in EDTA anticoagulant tube (blood: EDTA = 5:1) from the participants in the study, then placed it in the refrigerator (-70 ℃), and extracted DNA and parted after three months. All these data were analyzed by the software of SPSS24.0 and Amos 24.0. The result shows that: (1) Negative life events, Internet addiction and college students' depression were significantly correlated with each other; (2) Internet addiction plays a partial mediating role in the influence of negative life events on college students' depression;(3) 5 - HTR1A gene rs749098 polymorphism moderated the direct path and the indirect path from Internet addiction and college students' depression. Compared with C/G and G/G genotype individuals, negative life events of individuals with C/C genotype had a stronger negative prediction of depression. Furthermore, in low levels of Internet addiction circumstance, individuals with C/C genotype showed higher depression, and all genotypes showed high levels of depression in low levels of Internet addiction circumstance. The current research adopts the research paradigm of depression’ genes and the environment (G *E), with depression susceptibility quality 5 - HTR1A gene rs749098 and social psychological factors (negative life events and Internet addiction), and build a moderated mediation model. The current research enrichs the theory of depression development and is also the important practice prevention and intervention of college students' depression.