For the reason to improve the sit and reach ability of students, effectively, the Department of Physical Education of Chung Shan Medical University has combined the key elements of three training methods (Static Stretching, Dynamic/Kinetic Stretching and Static-Passive Stretching) to create ”Interactive and Gradual Stretching Activity”. The sample were came from 96 year first semester female students, who had physical education class during 10 O' clock to 17 O' clock every Tuesday. The experimental group was formed by 56 female students, and was trained by Interactive and Gradual Stretching activity. The control group was formed by 56 female students, was trained only by regular stretching activity. After a semester, compared the sit and reach test results between pre-test and post-test from both groups. The experimental group was improved 5.33 cm, averagely (p＜.01), the results of flexibility test were achieved the significant level. The control group was improved.74cm, averagely (p＞.01), the results of flexibility test did not achieve the significant level. In the pro-test the flexibility test difference between experimental group and control group is 2.1cm, averagely (p＜.01), a significant relationship was found. Moreover, compared with the post-test between experimental group and control group, the difference is 6.68cm, averagely (p＜.01), a significant relationship was found. This study found, the female students of control group could not improve the flexibility by doing regular stretching activity, the female students of experimental group, who was training by the Interactive and Gradual Stretching activity, which supports the theory of summation of twitches, female students' flexibility can be improved effectively.