The friction which plays an essential role on normal contact stiffness is usually omitted in existed researches, thus a modified fractal model for normal contact stiffness considering friction is discussed in this paper for calculating normal contact stiffness precisely and reasonably. The model is obtained by introducing a specific coefficient factor into the equation of the normal contact stiffness which is deduced by employing the theory of fractal contact and the definition of stiffness. Through the simulation and comparison with the original model and experiment result, it is clearly concluded that the modified model can reveal the influence of friction on contact area as well as calculate the normal contact stiffness more accurately. Furthermore, the numerical results show that the normal contact stiffness increases with the normal load; it is advantageous to improve the normal contact stiffness of rough surface by adding fractal dimension-D and reducing fractal scaling parameter-G. Also, the friction coefficient decreases with adding D and G and the fractal dimension has a marked impact on the friction coefficient. The presented achievements will help to analyze the performance for surface contact dynamics in the future. (C) 2015 Elsevier B.V. All rights reserved.