The invention discloses an antiresonant three-phase four-wire integrated casting insulated mutual inductor. In the mutual inductor, terminals of primary winding coils of three voltage mutual inductors are mutually electrically connected, and the other terminals of the primary winding coils are respectively connected to primary connecting terminals; winding coil measuring tail ends of secondary sides of the three voltage transformers are mutually connected and used as grounding ends, and start ends thereof are respectively connected to secondary connecting terminals; protective winding coils of the secondary sides of the three voltage transformer are sequentially, serially and electrically connected in an opened triangle pattern, damping resistors are connected in series among the openings of the opened triangle, and output ends of the opened triangle formed by the serial connection are respectively connected to the secondary connecting terminals; and the three voltage mutual inductors are cast by insulation materials to form a fully enclosed casting body arranged in a shell. The mutual inductor can effectively absorb high order harmonic elements of secondary circuits by the damping function of the damping resistors so as to prevent the output circuit from resonance and prevent the transformer from being burnt down due to the ferromagnetic resonance.