Under the continuing action of temperature stress and load vehicle, the crack in cement stabilized aggregate base can easily reflect up into the asphalt surface layer, affecting driving condition and then affecting the fatigue life of pavement. On the basis of fracture mechanics, taking center crack loaded with uniform tensile stress as study state, methods were derived to calculate the stress intensity factor (abbreviated in the following “SIF”) of the crack at the bottom of asphalt layer using weight function theory and method of Petroski and Achenbach. Through the comparison of different SIFs under different conditions, factors affecting the SIFs such as crack length, load conditions, modulus ratio between base and surface layer and different jointed conditions were studied. To facilitate comparison, taking completely smooth and completely continuous as study boundary conditions. According to calculation results, factors mentioned above all influence the SIF values of the crack at the bottom of asphalt layer greatly, among which jointed condition between base and surface layer has the most important influence. The SIF values of the completely smooth interface is several times that of the completely continuous interface. We can take measures to improve the jointed condition between the asphalt surface layer and the cement stabilized aggregate base thus can reduce reflection crack effectively.