Establishing human body dynamics model to obtain human natural vibration frequency is a common scientific challenge in various fields such as civil engineering， traffic engineering， aerospace， rehabilitation medicine and so on. The spring-mass-damper （SMD） model is most commonly used in previous studies， which actually is not consistent with the distribution characteristics of human mass and stiffness along the height. In this study， a distributed parameter dynamics model of the human body with a pair of biomechanical forces is proposed， and the analytical solution of human natural frequency is theoretically derived. Therefore， a fre? quency recognition method based on gait tests is proposed. 247 subjects are organized to conduct gait tests， and their stiffness and natural frequency are identified. The rationality and applicability of the proposed model are verified from multiple perspectives： by fitting the probability distribution of results， comparing the results with other researches， and analyzing the results across different age groups.