Posttraumatic stress disorder (PTSD) is considered to be an important psychopathological factor leading to individuals' addictive behaviors. Studies in the adolescent population are limited, though some studies have found that PTSD symptoms had positive effect on Internet addiction symptoms in elementary school and college. However, it is not clear about the mechanisms between PTSD symptoms and Internet addiction symptoms. Some researchers propose that the relationship between psychopathology and Internet addiction should be based on the role of motivation factors related to semotion. The Compensatory Internet Use Theory assumes that after experiencing stressful life events, many people attempt to reduce their resulting negative emotion by engaging in excessive internet use. But more evidences are needed to clarify what are the motivations conjunction with PTSD symptoms and how does these affect the relationship between PTSD symptoms and Internet addiction symptoms, and whether the effecting mechanisms are different in different gender groups. Therefore, Loneliness and sensitivity of punishment stimuli might mediate the relationship between PTSD symptoms and Internet addiction symptoms in post-earthquake adolescents as emotion-related motivational factors. In addition, the mechanism of these factors needed to be explored in different gender groups. Therefore, the current study aimed to explore the role of sensitivity of punishment stimuli and loneliness in the association between PTSD symptoms and internet addiction symptoms among post-earthquake adolescents of different gender 9.5 years after the Wenchuan earthquake. 767 post-earthquake adolescents (337 boys and 430 girls) were selected from 4 middle schools in the county of Wenchuan and Dujiang Dam city, the areas most severely affected by the Wenchuan earthquake. Participants completed the Revised Edition DSM-5 of Post-traumatic Stress Disorder checklist, Behavioral Inhibition System Scale, Loneliness Scale, and the Revised Chen Internet Addiction Scale. All the measures showed good reliability and validity in the present study. Data were analyzed using SPSS 21.0 and MPLUS 7.1, which was specifically developed for assessing the complex models including both mediators and moderators with the bias-corrected percentile Bootstrap method. After controlling age and repeated trauma exposure, the analysis of structural equation model found that PTSD symptoms had a positive effect on Internet addiction symptoms. The indirect effects of PTSD symptoms on internet addiction symptoms through sensitivity of punishment stimuli and loneliness were both significant. Moreover, PTSD symptoms could positively affect internet addiction symptoms by sensitivity of punishment stimuli via the chained mediating effect of loneliness. In the girl group, PTSD symptoms not only had direct effects on internet addiction symptoms, but also had indirect effect on internet addiction symptoms through sensitivity of punishment stimuli and loneliness respectively. However, PTSD symptoms only had direct effect on internet addiction symptoms in boy group. The present study demonstrates the impact of PTSD symptoms on post-earthquake adolescents’ Internet addiction symptoms, as well as the mediating roles of two motivational factors related to emotion (sensitivity to punishment stimuli and loneliness) underlying this relation. The moderating effect of gender in the mediation model is discussed. These findings may contribute to a better understanding of the effects, mechanisms, and the gender differences on internet addiction symptoms among post-earthquake adolescents. The implications of our findings for the intervention of post-earthquake adolescents’ Internet addition symptoms are also discussed.