The online learning has gradually become a notable trend of K-12 education, which requires students' continuous intention in regard to online learning. Although it is acknowledged that both environmental, technological, and personal factors have the potential to enhance students' continuous intention toward online learning, there is limited knowledge regarding how these factors interact with each other to affect students' intention to engage in online learning continuously. Therefore, this study proposed a moderated mediation model to investigate the relationships among K-12 students' perceived teacher support, perceived technology usefulness, perceived interest, and continuous intention relating to online learning. A total of 1363 valid questionnaires were collected. We found that the extent of teacher support positively predicted students' intention to continue online learning, but this effect was fully mediated by perceived technology usefulness. Moreover, the mediating path among teacher support, technology usefulness, and continuance intention was moderated by perceived interest. The moderating effect on perceived technology usefulness was higher for students with a low sense of perceived interest than those with a high sense of perceived interest. In light of these findings, it was suggested to establish teacher support that could stimulate technological advantages and pay attention to the cultivation of students' interest to enhance their continuance intention toward online learning. The limitations and future research directions were discussed.