Maintaining functional ability and independence are essential in the healthcare of older adults. Physical activity(PA) has been acknowledged as effective and economical health promotion strategies in older population. However, the amount of PA needed to maintain functional ability in older adults remains unclear. This investigation used PRISM Dose-response Curves Stimulation Variable slope model to explore the relationships between the amount of PA and functional ability in community-dwelling young-old, middle-old and old-old age group adults. ANOVA analysis was used to examine the relationship between functional ability and self-perceived active level changes compared to 10 years ago. NHANES 2005-2006 older participants datasets were used. The study found positive dose-response curve relationship in middle-old female adults. Older women aged 75-84 years benefit from every minute spent on PA, an amount of 150 minutes per week is necessary to obtain the most functional benefits. Older adults who are 65 years old and above need to walk 5,400 -6,500 steps per day or spend 1,500- 4,500kcal energy, or 150-450 minutes per week on PA to maintain their functional abilities in later ages. Older adults who perceive themselves less active compared to 10 years ago have more difficulties in doing daily activities than those who considered themselves the same active levels.