Abstract: The wavefront power spectral density (PSD) can give the spatial frequency distribution of wavefront aberration, limit the waviness and the roughness, and specify the large components employed in high power density solid-state laser for inertial confinement fusion (ICF). The definition and the calculation of the PSD are given in this article. In experiment, a large phase shifting Fizeau interferometer was used to test the transmis sive wavefront of a Nd glass, creating the one dimension wavefront PSD. Same time, relationship between the PSD and the RMS is shown in the paper.