The deducible process was given to solve the probability distribution density associated with an individual asperity contact spot of area a. The probability distribution density is applicable to the mechanical processing rough surface in spite of grinding, milling or turning. The approach of computing the fractal dimension and fractal roughness was embodied from the structure function of whole flexible joint surface. The theoretical computation and analysis from reference [1] were quantitatively experimentally validated. The experimental evidence displays that under a certain condition of normal loading heavy object, the absolute warp between the theoretical static friction coefficients and experimental ones distributes from -0.03302 to 0.01926, and the relative windage between them fluctuates from -8.323% to 5.512%.