This paper proposes a reduced 1D model for the full wave simulation of SAW in high speed with improved accuracy. Simplifications underlying the traditional coupling-of-modes model are introduced to the full wave analysis of the device structure supporting the Bleustein-Gulyaev-Shimizu wave. Then a 1D equation with respect to the surface charge to be solved is derived. The synchronous IDT structure is analyzed. In the case, the strip admittance is given in a closed form, and it can be reduced into a form given by Koskela, et al, which is known to offer good accuracy for the simulation of SH-type SAWs.