Generally speaking, the asphalt concrete pavement will be affected by the temperature and aging when it is in the use, which makes the modulus of asphalt mixtures change as non-uniformity gradient. This paper assumes the different changes on the modulus of surface layer with different gradient and then researched the mechanical characteristics of asphalt concrete pavements with cracks and no cracks by the finite-element method . Moreover, the research focused on the stress and K I & K II of the asphalt concrete pavements affected by the modulus of surface layer changed as non-uniformity gradient. The results demonstrated that the larger the gradient on the modulus of the surface layer,the bigger the tensile stress and K I and K II of the asphalt concrete pavements, and K II is even much bigger than K I. Consequently, it is of great importance to take into account the effect of the modulus of surface layer changed as non-uniformity gradient. It also makes a great significance for the revision of pavement design and the analysis of pavement damage mechanism.