Problematic social media use is detrimental to users' subjective well-being. Based on cognitive behavioral therapy (CBT), we proposed a short-term abstinence intervention to treat this problem. A mixed method study with 65 participants was conducted to examine the effectiveness of this intervention and to reveal the underlying mechanisms of how the intervention influences participants. While the experimental group (N = 33) took eight 2.5-h breaks from social media over two weeks and had daily dairies, the control group (N = 32) used social media as usual and had daily diaries. The results demonstrated that the intervention has a positive effect on life satisfaction. The effect varied with the time users conducted abstinence (work hours vs. off hours) and the level of social media addiction (heavy users vs. normal users). Qualitative findings from dairies and interviews unveiled associations among users' behaviors, feelings, and cognitions during and after abstinence. These results extend the understanding of the CBT-based short-term abstinence intervention and suggest opportunities to alleviate problematic social media use.