In order to properly evaluate the impact coefficient of heavy transport vehicles passing through tied-arch bridges, this study takes an 80 m-span tied-arch bridge as an example. Based on the ANSYS platform, a vehicle-bridge coupling model under the load of low-speed heavy transport vehicles is established. By analyzing the vibration characteristics of the vehicle-bridge coupling system, the influence of vehicle speed and load on the impact coefficient of the bridge is discussed. The results show that even when the vehicle travels at a speed of 2 m/s under Class B roughness, the maximum impact coefficient reaches 0.061 when the vehicle is 4 m/s. When evaluating the passage of heavy transport vehicles over tied-arch bridges, the impact effect should be considered even at low speeds. The influence of vehicle load on the internal force impact coefficient of tied-arch bridges is greater than that of the displacement impact coefficient. When the vehicle load is large, the impact on the bridge is small, but an excessive increase in vehicle load will increase the burden on the bridge. A load of 400 t is considered a more ideal value.