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.