The principle of phase discrepancy compensation of the tetragonal OCT (Optic Current Transducer) sensor head with dual layer optic circuit is analysed as well as its existing proplem. A new kind of the OCT sensor head is designed, of which the structure is simpler and the performance is better. It is demonstrated that the phase discrepancy caused by optical dispersion of this new kind sensor head is very small and its influence on measurement can be ignored, showing practical significance.