Objective To promote the comprehensive development of physical condition of middle school students,this study combine with the sunlight sports and carry out the scientific experiments from the perspective of improving flexibility.Methods This paper selected 125 students of the 91st Middle School in Xi'an took part in 10-week BODY-BUILDING JOINTS EXERCISE which as the main exercise of the fitness program,then studied the indexes of the participants on flexibility as well as balance before and after the exerc...