Based on fractal geometry theory, a root-mean-square(RMS) wavelength method was proposed to quantitatively evaluate a 3D stochastic surface topography, by means of the surface spectral moments. Through DFT of the profile measured by a Talysurf-10 contact stylus instrument, we obtained the power spectrum and thefractal dimension of the profile. Further, the zero and 2nd order spectral moments of the profile and the surface were obtained. Using these parameters, the evaluation of RMS wavelength was conducted. By experiments for ground samples, the validity of the present method was confirmed.