In order to explore the simplified calculation method of pier bottom shear considering the contribution of seismic inertia force of pier， a three-dimensional finite element model of a railway simply supported beam bridge was established. Based on the analysis of the influence of pier mass on structural dynamic characteristics， the contribution proportions of pier inertia force to seismic shear force at pier bottom under different height of bridge pier， site type and peak ground acceleration （PGA） were studied with nonlinear time history analysis method. The criterion of inertia force of pier which can't be ignored in calculating seismic shear of pier bottom was also suggested. The modal pushover analysis method is used to simplify the calculation procedure of pier bottom shear， and its accuracy is also verified. The results show that when the pier was in plastic stage， the contribution of inertia force to the shear force at the bottom of the pier was seldom affected by the site type， and the key influence factor was the pier height.When the pier height was less than 20 m， the inertia force of the pier could be ignored， and the shear force demand at the bottom of the pier could be calculated by the concept of capacity protection. However， when the pier height was larger than 20 m， the contribution of inertia force of the pier itself should not be ignored. The shear force demand at the bottom of the pier could be obtained by the proposed first-order modal Pushover simplified method.