In this study, a B41 band SAW filter was designed, and SMD and CSP packages were modeled using 3D electromagnetic field simulation software. The acoustic-electromagnetic simulation results of the two packages were compared, leading to the preliminary conclusion that, for the topology of the filter circuit, the out-of-band rejection at high frequencies may increase (warping “upward”) when two different parallel branches are connected.This effect is due to the electromagnetic parasitic parameters of the bonding leads in the SMD package. SMD package models were established and simulated with varying numbers, diameters, and lengths of bonding wires to calculate the S-parameters. The simulation results indicate that as the diameter of the bonding wire increases and the length decreases, its equivalent inductance becomes smaller. Consequently, the electromagnetic parasitic parameters of the bonding wire decrease, reducing their influence on the performance of the SAW filter, and optimizing the outof- band rejection performance at high frequencies. Additionally, the ball-implanted inverted button of the CSP package exhibits smaller electromagnetic parasitic parameters, resulting in better joint acoustic-electromagnetic simulation outcomes, which align well with the measured results.