Currently, due to decreasing number in birth rate, parents have the tendency to overprotect their children; unknowingly hindering children's chance to be active. Compounding with the factors of bad eating habit, chronic diseases started to affect our children at a much younger age and threaten their health. This research studied the relationship between elementary school students' life style and their BMI abnormality. The study subjects were six graders of Gongguan Elementary School in Miaoli County and the data were collected by means of stratified-cluster random sampling. Using self-designed structural questionnaires, 358 effective questionnaires were collected and the retrieval rate was 88.7 %. The SPSS analysis software system was employed to run descriptive statistic, one-way ANOVA, and Path Analysis. The major findings of this study are as follows: the students' life style is positive; the students' life style is affected significantly by their parent's exercise habit and the types of activity parents enjoyed during their leisure time. The key observation factors of BMI abnormality, in addition to the students' eating habit, including the following: excise and leisure activities, attitude toward BMI management, and actions toward BMI management. Through the findings, we strongly urge the NCC to implement a regulation regarding junk food commercial supervision on TV; to lower the exposure rate of junk food commercial to children; to encourage students to exercise and expend their leisure activities; to reduce the length of static activities; to implement health education effectively; to build a feasible model for school and parents to work together.