The invention discloses an open type fault transient current sensor which comprises a first semi-ring body and a second semi-ring body, wherein a wire is wound to the tail end of the first semi-ring body from the head end of the first semi-ring body according to the first winding direction and then wound back to the head end of the first semi-ring body from the tail end of the first semi-ring body according to the first winding direction; the head end of the first semi-ring body and the head end of the second semi-ring body are spliced, the tail end of the semi-ring body and the tail end of the second semi-ring body are spliced to form a complete ring; the wire is wound behind the tail end of the second semi-ring body from the head end of the second semi-ring body according to a second winding direction opposite to the first winding direction, and then wound back to the head end of the second semi-ring body from the tail end of the second semi-ring body according to the second winding direction; and the conductors wound on the first semi-ring body and the second semi-ring body are both provided with a winding starting end and a finishing end, the two finishing ends are connected with each other, and the two starting ends are output ends. The open type fault transient current sensor is convenient to install, and the influence on the interference of a magnetic field in vertical direction can be eliminated.