The invention discloses a merging unit with a protection current transformer output abnormity detection function. The merging unit comprises a protection current transformer and a zero sequence current transformer which are respectively used for collecting A, B and C three phases of protection currents and a zero sequence current; the protection current transformer is connected with the A, B and C three phases of protection currents of an electric power system and outputs the three phases of currents to the zero sequence current; Break variables of phase currents and zero sequence current break variables are calculated; the calculated phase current break variable result is compared with the zero sequence current break variable result; the merging unit merges the A, B and C three phases of protection currents into a self-produced zero sequence current, sampling point instantaneous value inconformity discrimination is carried out on the self-produced zero sequence current and an external zero sequence current, and sampling point instantaneous value comparison is carried out on the self-produced zero sequence current and the external zero sequence current, so that output data abnormity of the protection current transformer can be determined rapidly, data is rapidly marked as fault data, and a transformer substation protection control device is prevented from making wrong judgment due to interference of abnormal data.