In this paper, the propagation characteristics of the surface acoustic waves based on ScAlN/6H-SiC structure is studied by using the finite element method. The influences of the piezoelectric materials thickness change on the phase velocity and electromechanical coupling coefficient of SAW in ScAlN/6H-SiC structure under four kinds of exciting conditions is analyzed. The electromechanical coupling coefficient is optimized again by changing the electrode thickness and metallization ratio. The results show that the electromechanical coupling coefficient of IDT/ScAlN/6H-SiC structure can reach 5.4%, and the corresponding phase velocity is 6.36 km/s. After adding short-circuit metal, the electromechanical coupling coefficient and phase velocity have been improved. The optimized electromechanical coupling coefficient and phase velocity of SAW in metal/ScAlN/6H-SiC structure are 15.78% and 7.33 km/s, respectively.