At present, the dynamic amplification coefficient of bridges defined in domestic and foreign codes cannot fully reflect the influence of various complex factors on the dynamic performance of bridges. In the design stage, it is a normal state for every bridge to be calculated. Accordingly, this article established the high-speed train-trackbridge coupled vibration system model to analyze the dynamic characteristics of 33 bridges under different vehicle types and speed loads. Based on the probability statistics theory, the concept of spectral function was introduced, taking the natural vibration period of structure as the index. The function expression suitable for calculating the dynamic amplification coefficient spectrum of the bridge structure under vehicle bridge coupling was obtained at a certain guarantee rate. Another 10 bridges were selected for vehicle-bridge coupling calculation to verify the applicability of the dynamic amplification coefficient spectrum method. The results show that the method has certain guarantee rate and applicability. Finally, some suggestions are given to improve the accuracy of the method.