Abstract: Bridge modal parameters are not only related to structural characteristics but also vulnerable to temperature change. The modal variation of bridges due to temperature effect can even overshadow the alteration in structural dynamic characteristics resulting from structural damage. Thus, exploring the influence of temperature on the dynamic characteristics of long-span continuous rigid frame bridges is of great significance for the accurate assessment of structural health conditions. Taking a four-span continuous rigid frame bridge as the target structure, the dynamic finite element model was established to obtain the natural vibration characteristics of the structure, and the accuracy of the model was verified based on the measured modals. The bridge structure temperature was obtained based on a three-dimensional thermal analysis model, enabling the calculation of the dynamic characteristics of the long-span continuous rigid frame bridge under variable temperature conditions. Subsequently, the degrees of change in the dynamic characteristics of the bridge caused by factors such as elastic modulus, longitudinal deformation of the main girder, changes in constraint stiffness, bearing icing, temperature internal forces, and comprehensive influences were quantified. Finally, based on these quantitative results, the influence mechanism of temperature effect on the dynamic characteristics of long-span continuous rigid frame bridges was summarized, and the main factors leading to the frequency change of this type of bridges under temperature effect were given. The results indicate that the change in concrete elastic modulus contributes over 90% to the change in the natural frequency of structure. The change in compressive stiffness is the main cause of the change in structural frequency due to the change in bearing stiffness. Temperature-induced initial shear force, bending moment, and torque have no impact on the structural frequency. The fundamental frequency of the structure is most significantly affected by the annual ambient temperature changes, with the frequency change range being -2.09% to 2.04%, and the change rates of all the other four order frequencies within ±2%.