Although the flipped pedagogical approach has been exhaustively explored, the effect of video length remains sparsely studied. Through a mixed design, videos, and three ratio scales, this study determined the effect of video length on English proficiency, student engagement, and satisfaction in a flipped English classroom in China. We concluded that: (1) The short video (shorter than 5 minutes)-assisted English flipped classroom could lead to significantly higher English proficiency, student engagement, and satisfaction than the flipped classroom assisted with medium videos (10-20 minutes); and (2) The medium video-assisted English flipped classroom could lead to significantly higher English proficiency, student engagement, and satisfaction than the flipped classroom assisted with long videos (longer than 30 minutes). Designers of videos could make every effort to provide short videos to improve English proficiency, engagement, and satisfaction. They could also seriously consider a scale, a mobile platform, quizzes, pictures, and multimedia in the future design and innovation of videos.