Tuned mass damper (TMD) in the engineering application is sensitive to a frequency which is difficult to adjust. In light of this problem, this paper proposes an adaptive-passive TMD. It includes, besides the damper, the variable mass, spring, servo control system, and driving system. The servo control system consists of an acceleration sensor and a single chip computer circuit board which is used to receive the structural acceleration sensor signals under ambient excitation. The short-time Fourier transform (STFT) is used to identify the first order natural frequency of the structure and adaptively change the quality of the TMD to adjust the frequency of TMD and recognize the frequency of the main structure. The feasibility, reliability, and validity of the adaptive-passive TMD are verified by the pedestrian bridge model test. The experimental results show that the adaptive-passive TMD can accurately identify the vertical vibration frequency of the model structure and retune its frequency to the same frequency. Freedom vibration tests and forced vibration tests show that compared with the mistuned TMD, the retuned TMD can improve the equivalent damping ratio of the pedestrian model, and reduce the peak acceleration response and root-mean-square (RMS) values.