The invention provides a three-phase power transformer parameter online identification apparatus and a realization algorithm thereof. An identification unit employs a parameter online real-time identification algorithm and comprises a fundamental wave extraction algorithm unit d, a vector orientation algorithm unit e and an instantaneous vector algorithm unit f. Primary fundamental wave electric signals and secondary fundamental wave electric signals are obtained from primary three-phase electric signals and secondary three-phase electric signals of a three-phase transformer through the fundamental wave extraction algorithm unit d, and the primary fundamental wave electric signals and the secondary fundamental wave electric signals are successively output to the vector orientation algorithm unit e and the instantaneous vector algorithm unit f. Real-time online identification on parameters of the three-phase transformer is realized through a real-time phasor method, the reliability and the accuracy of online parameter identification of the transformer are effectively improved.