The dispersion curves such as the phase velocity and electromechanical coupling coefficient(k2) were calculated theoretically in this paper. The result shows that Sezawa wave mode 1 on ZnO(c plane)/sapphire(cplane) structure has maximal k2 value of 2.705％ and phase velocity 4 982 m/s at h/λ=0.48, and Sezawa wave mode 1 on ZnO(a plane)/sapphire(r plane) structure has maximal k2 value of 4.34％ and phase velocity 5 509 m/s at h/λ=0.3, which means IDT/ZnO(a plane)/sapphire(r plane) structure has higher maximal k2 value and phase velocity of Sezawa wave mode 1.In other words,IDT/ZnO(a plane)/sapphire(r plane) structure is the better choice for designing high frequency and low loss SAW filter.