Health fitness is now commonly used to evaluate the health level of individuals. Among the four elements of health fitness, flexibility is often neglected. In fact, good flexibility is an essential element to ensure smooth movement and life without injury, especially for the elderly, good flexibility is a prerequisite for functional activities and directly affects the quality of life in later life. However, the current methods of flexibility-related measurement have problems such as unclear measurement base, no definition of measurement time, no description of measurement frequency, insufficient data accuracy, and complicated measurement tools. This study expects to construct a more scientific flexibility measurement system by redefining measurement concepts, expanding measurement methods in disguise, developing new measurement techniques, and developing professional measurement tools.