The type of I-II compound crack in bridge deck pavement is most popular. Based on the theory of fracture mechanics the least equivalent stress method is put forward and used to study the problem of concrete cracks. The method could be used to determine the fracture angle of I-II compound crack. For the cracked deck pavement, the stress state could be determined by field test or numerical simulation method and then calculate the equivalent stress near the point by Matlab. The examples show that when the equivalent stress gets to the critical value the crack will develop along fracture angle which could be calculated from the least equivalent stress method. The theory value of fracture angle is basically accurate with the test one.