This study got the following conclusion by applying and verifying the complex flexibility training program (static stretching, wave stretching, passive stretching) for 12 weeks to improve the flexibility of 13 national delegate boxers. In the item of static stretching, the value increased from 12.46±6.36cm (before applying flexibility training program) to 18.67±3.70cm (after applying flexibility training program) by 49.8%, showing statistically significant difference (p<.05). In the item of wave stretching, the value increased from 57.26±6.40cm (before applying flexibility training program) to 62.23±6.79cm (after applying flexibility training program) by 8.7%. In the item of passive stretching, the value increased from 135.91±13.50゚(before applying program) to 138.66±15.43゚ (after applying program) by 2.0%, without showing statistically significant difference. Considering this result, the flexibility training program for 12 weeks was found to have positive influence and the development of flexibility is judged to lead to the development of physical strength in muscular power, muscular endurance, etc.