The video length limit is an important operational design decision made by social media platforms. Many students and young adults are drawn to short-form videos on platforms like TikTok and Instagram. This study explores the role of present bias played in developing addiction. Through building and analyzing economic models, we theoretically demonstrate that present bias contributes to addiction. Viewers with high present bias are more likely to be addicted. Furthermore, we investigate how the short form of videos on TikTok interacts with present bias, and impacts addiction. We find that the short form extends addiction to viewers with lower present bias.  Our analytical model and results offer a theoretical explanation for the empirical observations on short-form video addiction.