In recent years, owing to the development of mobile devices, people can use social media more conveniently. This new trend of media drastically changes people’s lives, especially among adolescents. Earlier researches suggested it benefits their learning performance but also contains the risk of addiction. This research thus investigated the relationship between the usage of social media and the academic achievement of college students, and whether this would be different among students with the various locus of control. There was a total of 298 students participated in this research. The results are as follows: (1) External locus of control on expanding one’s conduct grade has several significant positive effects. (2) External locus of control on expressing the usage of social media has several significant positive effects. (3) Conduct grade was directly affected by External locus of control, this connection was the full mediation by the use time of social media. Last but not least, we have some suggestions for teachers, parents, and schools. Since using social media is essential for modern life, the following rise and problems from using social media applications or websites exist too. However, social media should not take the blame entirely. It all depends on how you use it. We should teach students to control themselves and use the right way to get better academic results, rather than getting rid of mobile phones and removing social media applications from their mobile phones. We hope that we can find the proper solutions in the future by having more in-depth research and avoid students’ abuse of social media and improve academic achievement.