The purpose of the study is to discuss the influence of rope skipping in junior high school's male and female students Body Mass Index (BMI). The subjects were 63 seventh graders, divided into a male group and a female group, who skipped rope twice a week for twelve weeks. They all took a pretest in physical fitness before training. The average high of 32 male students is 157.95±8.00cm and the average of weight is 52.52±14.54 kg; the average high of 31 female students is 154.89±5.34 cm and the average weight is 45.73±8.47 kg. With dependent t-test, the test data was used to check if there was any difference between the pretest and the posttest; the significant level was set at p＜ .05. After analyzing the data, the study concludes that there is a significant difference in male students in respect to Body Mass Index, flexibility (Modified Sit and Reach Test), explosive strength (standing long jump) and cardio-pulmonary endurance (800/1600 meters running). From above conclusions we make some suggestions, the first is that excise should last long enough to improve the balance of body composition in order to enhance cardiovascular function. The second is takes some full body stretch activity, without take up lot of space. The third is due to different student's background to set different excise frequencies in order to improve training efficiency.