Accurate and simple measurement method for the thermal diffusivity of high-conductivity thin film is required for the design of very densely packed integrated circuits such as ULSI. In order to measure the thermal diffusivity of high-conductivity thin film such as graphite and diamond, a new apparatus based on a dynamic grating radiometry (DGR) has been developed. In DGR method, a sample surface is heated by interference of two pulsed laser beams, and the decay of temperature at a spot on the thermal grating is monitored by an infrared detector. In the ideal case where the grating period is much smaller than the light absorption length, the thermal diffusivity parallel to the surface can be determined from the decay constant and the grating period. To consider the two dimensional problem, the anisotropy of the thin film is detected by DGR. In this paper, the theory which can calculate the thermal diffusivity perpendicular to the plane is presented. The validity of DGR is discussed through the preliminary measurement for Zr foil and Graphite Sheet.