Abstract: A basic method to measure the random variable of runway roughness according to roughness criteria based on power spectral concrpts is derived.The power spectral criteria are primarily used for consideration of aircraft fatigue.According to the theory of generalized harmonic analysis, the power spectral analysis for random processes must be assumed to be stationary, ergodic and to agree with Gaussian distribution. On this assumption,a power spectral curve which provides description of frequency characteristics of roughness for a runway was calculated step by the method decribed in reference 2.The we considered the landing gear and its airframe taxiing on the rough runway as a system with multi-degrees of freedom and derived the simultaneous differential equations of motion by using Newton's second law.For simplicity, we used the model matrix as transformation matrix to uncouple the simultaneous differential equations into a set of independent equationsAlso,the method of determining transfer function by means of solution of eigenvalue problems was considered.At last,the carves of exceedances per flight vs the incremental accelaration of airplane during taxiing were introduced.