The change of the Rayleigh surface wave velocity on Y-cut Z-propagation (YZ) $LiNbo_3$ is measured by schlieren method and phase shift method. It is observed that the change in Rayleigh wave velocity is 3-13% by the mass loading effect of gold film as the thickness of film varies 1-3 μm, and that the change is 2% by electrical short of $LiNbo_3$ surface. The coupling constant of YZ $LiNbo_3$ calculated from the above result is 0.04. And the temperature dependence of the surface wave velocity (the change in Rayleigh wave velocity), $\frac{1}{V}\frac{\partial{V}}{\partial{T}}$, is measured to be $-8.8\sim-8.86\times10^{-5}$/℃ within the range 0℃∼80℃. And the temperature stabilty of $LiNbo_3$, $\frac{1}{\tau}$ $\frac{\partial\tau}{\partial{T}}$ is measured to be $9.3\times10^{-5}$/℃.
The diffraction phenomenon by the surface acoustic lens made on the tangential plane is observed. Diffraction effect by the acoustic lens aperture is easly observed because the acoustic wave length is longer than that of light.
