The invention relates to a frequency domain analysis method of bridge fatigue life on the basis of a dynamic weighing system. The frequency domain analysis method comprises the following steps: collecting data including the vehicle weight, the vehicle speed and the axle distance of each vehicle which passes through a bridge; calculating the collected data, and carrying out curve fitting; according to a fitting probability density curve, establishing a cellular automata simulation model of the vehicle, and generating a random traffic flow; simulating load time history under different vehicle flow density conditions, and loading the load time history to a bridge influence line to obtain stress time history data; carrying out FFT (Fast Fourier Transform) on the stress time history, obtaining PSD (Power Spectral Density), and calculating relevant parameters; using a Dirlik method to establish an experience form of a PDF (Probability Distribution Function); and calculating residual service life. Calculation time is greatly shortened.