By using a Maon——Zehnder inter ferometer and an optical delaying system, we made a time-resolved multi-frame interference recording for the plasma on dielectric thin films produced by YAG laser. We have calculated the electron density and plasma shock speed from the series of interforograms, and firstly acquired relevant results about 15 ns pulse width (FWHM) of 1.06 μm laser interacting with dielectric thin films within 150 ns.