In this study, a B41 band SAW filter was designed, and SMD and CSP packages were modeled using3D electromagnetic field simulation software. The acoustic-electromagnetic simulation results of the two packageswere compared, leading to the preliminary conclusion that, for the topology of the filter circuit, the out-of-band rejectionat 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 packagemodels were established and simulated with varying numbers, diameters, and lengths of bonding wires to calculatethe S-parameters. The simulation results indicate that as the diameter of the bonding wire increases and thelength decreases, its equivalent inductance becomes smaller. Consequently, the electromagnetic parasitic parametersof 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 packageexhibits smaller electromagnetic parasitic parameters, resulting in better joint acoustic-electromagnetic simulationoutcomes, which align well with the measured results