Abstract: In order to effectively analyze the crack propagation in asphalt pavements, three geometric functionsF(a/b)for analysis of bottom cracks in asphalt layers are yielded by fitting some discrete values of crack lengths. These discrete values with different ratios of crack lengthato asphalt thicknessbare obtained based on the stress intensity factors calculated by finite elementmethod (FEM) with the crack face being subjectto a uniformstress. The three geometric functions are verified respectively underothertwo sets of loads. The stress intensity factors produced by the three geometric functions according to the theory of weight function are in good agreement with those calculated by FEM in the whole calculation fields. In addition, the weight functions in the whole calculation fields are obtained using the three geometric functions, and a comparison between the weight functions is made