Abstract: To investigate the wave load on both circular and rectangular bridge piers under tsunami wave effects, a second-order nonlinear Morison equation was derived based on the Morison equation and the second-order solitary wave theory. Numerical simulations were conducted to study the distribution characteristics of wave forces on bridge piers. By considering the influence of wave action above the still water level, empirical formulas for the wave force coefficients, C_D and C_M, were proposed, and an improved second-order nonlinear Morison equation was established. The accuracy of this improved equation in calculating wave forces on circular and rectangular piers was verified through a comparison with numerical simulation results. The results indicate that considering the wave height effect significantly improves the accuracy of wave force predictions using the second-order nonlinear Morison equation. The wave force coefficients C_D and C_M are primarily related to the ratio of wave height to water depth H/d. When H/d is within the typical range of 0.15-0.55, empirical formulas for C_D and C_M are obtained based on the least squares method. Further the comparison with numerical simulations confirms that the improved second-order nonlinear Morison equation can accurately compute the wave forces on both circular and rectangular bridge piers. The findings provide valuable insights for estimating wave-induced forces on bridge piers under tsunami-like solitary waves.