The slow traffic system of the bridge crossing the river is of great significance to improve traffic quality and traffic safety. The long-span medium-bearing tied arch bridge with roadway on the upper floor and the slow traffic system on the lower floor is a novel structural form. In order to analyze the vehicle-induced vibration comfort of the slow traffic system, taking the Jiulonghu bridge in Nanchang city as the background, the random traffic flow is generated based on the multi-lane traffic flow distribution and S-shaped speed density model, and the vibration response of the sidewalk position was solved by the modal superposition method and the Runge-Kutta numerical integration method. According to the ISO 10137:2007 standard, the vibration response is evaluated, and the results showed that the vibration of the slow traffic system of the bridge was mainly vertical under the action of random traffic load. Under the condition of mild congestion, the vertical vibration acceleration reaches the maximum, with a peak value of 0.34m/s² , and the corresponding three-direction comprehensive maximum acceleration RMS value is 0.0982m/s² , which meets the "no discomfort" standard stipulated in the ISO 10137 code, but the vibration of the slow traffic system has a significant amplification effect compared with the vibration at the same position of the roadway. The proposed analysis methods and results can be used as a reference for the design of similar bridges.