The invention discloses a dynamic bridge parameter extracting system and a dynamic bridge parameter extracting method based on laser Doppler and relates to the technical field of bridge detection. The dynamic bridge parameter extracting method includes the steps of S1, collecting photoelectric signals of a photoelectric detector by a high-frequency signal collector, and converting the photoelectric signals into voltage values to obtain a photoelectric signal discrete sequence ; S2, by the aid of a computer, subjecting the photoelectric signal discrete sequence to fast Fourier transform so as to obtain a frequency movement sequence, seeking the specific position of the photoelectric signal corresponding to a peak value of the frequency movement sequence, subjecting a frequency-subdivided interval to further subdivision to compute a frequency spectrum within the frequency-subdivided interval, seeking the specific position of the photoelectric signal corresponding to a peak value of a frequency spectrum sequence, and computing a Doppler frequency shift; S3, computing moving speed of an object; S4, judging whether vibrating frequency of the object needs to be computed or not; S5, computing the vibrating frequency of the object according to a speed sequence. The dynamic bridge parameter extracting system and the dynamic bridge parameter extracting method based on the laser Doppler are high in extracting precision and used for measuring the low moving speed and the vibrating frequency of an engineering structure like a bridge.