As a normal life phenomenon, hypocotyl elongation is the result of long-term natural selection as well as a necessary prerequisite for photosynthesis and autotrophy. However, leggy seedlings are weak and have poor adaptability for overelongated hypocotyls, which negatively affects yield and quality improvement. This review summarizes research and development progress, the cytological mechanism of hypocotyl elongation and the molecular regulatory mechanisms of hypocotyl elongation by hormones and environmental factors and overviews the direction of future related research.