In order to calculate the misalignment of spiral bevel gears in the working conditions,the relationshipamong different groups of misalignment which lead to the same contact pattern is analyzed.It is found that thesegroups of misalignment are equivalent,and the misalignment identification can be solved by getting only one equi-valent solution without exact calculation.Then,the digital features of contact pattern are extracted,and the equiva-lent misalignment is obtained using an optimal method by means of minimizing the sum of two contact path devia-tions as the objective function.Finally,the precision of the identification algorithm and the effectiveness of theequivalent misalignment are verified by taking a couple of spiral bevel gears as an example.