The electron density of excimer(XeCl, 308nm) laser-produced plasma near the surface of Y-Ba-Cu-O target has been diagnosed with laser interferometry. The results showed that the electron density is about 1016-1017/cm3 when the laser power density is 3×108W/cm2 and the background pressure is 1.33-13.3Pa. And laser interferometry is an effective means for diagnosing temporal plasma parameters, and high diagnostic accuracy and spatial resolution can be obtained using the detecting laser beams with long wavelength. The experimental setup was described. Experimental results were discussed.