Abstract—Generally, students with intellectual disability are not good at athletic, since they have poor balance abilities. The problem causes a bad influence for their daily life and future work. The objective of this paper is to investigate what causes this situation by measuring balance capability with Zebris FDM-System. For comparison, normal college students are also chosen as subjects for the testing. The balance test types include standing with the eyes opened and the eyes closed, and disturbing balance by rotation scheme. The indexes including BMI, leg length and footprint area are adopted as physical conditions. The T-test is used to study the significant differences between normal students and mental disability students (MDs). The results show that there are significant differences in some balance ability index between the students with mental disability and normal students. More importantly, this paper uses correlation and Grey relation to find out the relationship between balance ability and physical conditions. The results by Grey relation show BMI is the most relevant condition influencing equilibrium. However, the correlation measurement reflects that there is significant relevance just for some index.