Aims This study aimed at evaluating the effect of family factors on the occurrence of Internet addiction and determining whether Internet addiction could make any difference in the family function. Methods A total of 2293 adolescents in grade 7 participated in the study. We assessed their Internet addiction, family function, and family factors with a 1‐year follow up. Results In the prospective investigation, inter‐parental conflict predicted the incidence of Internet addiction 1 year later in forward regression analysis, followed by not living with mother and allowance to use Internet more than 2 h per day by parents or caregiver. The inter‐parental conflict and allowance to use Internet more than 2 h per day also predicted the incidence in girls. Not cared for by parents and family APGAR score predicted the incidence of Internet addiction among boys. The prospective investigation demonstrated that the incidence group had more decreased scores on family APGAR than did the non‐addiction group in the 1‐year follow‐up. This effect was significant only among girls. Conclusions Inter‐parental conflict and inadequate regulation of unessential Internet use predicted risk of Internet addiction, particularly among adolescent girls. Family intervention to prevent inter‐parental conflict and promote family function and Internet regulation were necessary to prevent Internet addiction. Among adolescents with Internet addiction, it is necessary to pay attention to deterioration of family function, particularly among girls.