The invention relates to a method and system for detecting the initial phase of power signals. The method includes cutting a sampled signal sequence to obtained a shortened signal sequence, multiplying the cosine function of the measured reference frequency and sine function of the reference frequency respectively by the signal sequence and the shortened signal sequence to generate two sets of real frequency vector sequence and virtual frequency vector sequence, carrying out digital filtering on the two sets of real frequency vector sequence and the virtual frequency vector sequence to generate two sets of imaginary number vector filtering sequence and real number vector filtering sequence, generating two sets of imaginary number vector integral values and real number vector integral values, converting the two sets of imaginary number vector integral values and real number vector integral values into two phases according to preset phase conversion rules, and further converting two phases into the initial phase of the power signals according to the preset initial phase conversion rules. The initial phase with high accuracy is obtained.