The seismic response of long-span, continuous rigid-frame bridges is greatly affected by a parameter change. To further study the influence of various parameters of rigid-frame bridges on the internal force of the bridge under the action of an earthquake, the orthogonal numerical test method was adopted with a continuous rigid-frame bridge as an example. The transverse bending moment at the middle span of the main beam, the longitudinal bending moment at the pier top and bottom, and the transverse bending moment at the pier bottom were taken as the evaluation indices. The influence law of structural parameters (side span-to-central span ratio, power of beam bottom, pier height ratio) on the internal force of the bridge under seismic action, and the parameter sensitivity were analyzed. Results indicated that the pier height ratio had a great influence on the mid-span transverse bending moment. Additionally, it was observed that with the rise in pier height ratio, the maximum bending moment value increased by 28%. The side span-to-central span ratio had a large influence on both the longitudinal bending moment at the pier top and bottom and the transverse bending moment at the pier bottom, and with the increase of side span-to-central span ratio, the maximum value of the bending moment increased by 51%, 55%, and 52%, respectively. Bridge design in high-intensity areas should pay close attention to the choice of side span-to-central span ratio and pier height ratio.