The purpose of this research is that we analyze the changes of body composition and bone mineral density of overweight middle school boys after rope-skipping, examine the impact of regular exercise on the metabolism of bone mineral density, and offer the basis data for overweight middle school boys to do their exercise right, to promote their health, and to prevent osteoporosis. The research method: We made the overweight middle school boys in B metropolitancity skip rope for 8 weeks and measure the body composition and bone mineral density. The results are as follows. 1. The numerical value of the body fat has decreased from 31.09 % to 29.50 %. This is so meaningful in statistics. 2. The numerical value of body fat has decreased from 23.98 ㎏ to 21.67 ㎏. There is 231 ㎏ difference. This value is meaningful in statistics. 3. The numerical value of muscle has increased from 50.19 ㎏ to 51.50 ㎏. There is 1.31㎏ difference. This value is meaningful in statistics. 4. The numerical value of body fluids has decreased from 36.68 ℓ to 36.20ℓ There is 0.4ℓ difference which is not meaningful. 5. The bone mineral density of the lambar spine L2~L4 has increased from 1.152g/㎠ to 1.160/ g㎠. There is 0.008 g/cur difference which is not meaningful. 6. The femoral bone mineral density has increased from 1.125 g/㎠ to 1.154 g/㎠. There is 0.293 g/㎠ which is meaningful in statistics.