Bispectrum is an available method to analyze the quadratic phase coupling, non linearity and asymmetry of stochastic signal,whereas it has some obviously shortcomings,such as complex computation,lower estimation exactness and inconvenient vision.The ameliorated method of diagonal slice spectrum analysis is presented and used to characterize the skewness and phase coupling of the rough surface profiles.The experiment results show that the diagonal slice spectrum analysis technique is simple, effective and reasonable, and that it is possible to explain the change of rough surface spacing and amplitude parameter.