LiTaO₃ （LT） is an excellent candidate for piezoelectric substrates in surface acoustic wave （SAW）filters. To reduce the manufacturing cost and size of SAW filters, a 0.35 mm thick LT piezoelectric substrate needs to be replaced with one that is 0.25 mm thick. However, using the same design structure deteriorates the performance of the device. To address this issue, this article establishes an electromagnetic simulation model that includes chip bonding adhesive and simulates the electromagnetic characteristics of two different piezoelectric substrate thicknesses（0.25 mm and 0.35 mm） with varying adhesive thicknesses. The adhesive thickness is then optimized by combining electromagnetic and acoustic simulations to improve SAW filter performance. Finally, experiments show that by optimizing the adhesive thickness, the performance of the filter using the 0.25 mm piezoelectric substrate surpasses that of the original filter using the 0.35 mm substrate, thus meeting device specification requirements. This technical solution can be further extended to SAW devices using other piezoelectric substrates.