During　the　COVID-19　pandemic,　internet　use　and　gaming　of　adolescents　had　been　elevated.　On　the　one　hand,　internet　use　and　gaming　in　the　period　was　a　good　approach　to　killing　quarantined　time.　However,　the　increased　use　of　the　internet　and　game　of　adolescents　may　also　increase　the　risk　of　internet　addiction.　This　study　aimed　to　describe　the　internet　behavior　changes　of　adolescents　and　to　understand　the　impact　of　clinical　features　on　internet　addiction　after　the　adolescents　back　to　school　in　COVID-19　period.　We　conducted　a　cross-sectional　cohort　study　using　data　collected　through　online　investigation　in　China.　Six　hundred　and　twenty-five　adolescents　completed　the　online　survey.　Results　indicated　that　internet　addiction,　having　gaming　use　behaviors,　Strengths　and　Difficulties　Questionnaire　(SDQ)　Conduct　subscale　scores　and　the　SDQ　Prosocial　subscale　scores　before　the　COVID-19　outbreak　were　significant　in　predicting　the　internet　addiction　after　the　adolescents　back　to　school.　The　proportion　of　internet　addiction　and　gaming　behaviors　among　adolescents　in　China　was　changed　across　the　COVID-19　pandemic.　Clinical　features　before　the　COVID-19　pandemic　could　predict　Internet　addiction　risk　after　the　adolescents　back　to　school.