The utility model discloses an air-gap-type current transformer. The air-gap-type current transformer is characterized in that a theta-shaped iron core is adopted and is provided with three iron core columns; iron yokes are arranged at both ends of a left iron core column (1) and a middle iron core column (2) to form a magnetic flux loop; the left iron core column (1) is provided with a primary coil L1; the middle iron core column (2) is provided with a secondary coil L2; a right iron core column (3) is provided with a coil L3; the sum of the iron core section areas of the right iron core column (3) and the middle iron core column (2) is equal to or smaller than the iron core section area of the left iron core column (1); an air gap (4) is formed between the middle iron core column and the right iron core column. When the primary side current of the current transformer exceeds 200 percent of the rated current instantaneously, a great amount of magnetic flux of the current transformer penetrates to the right iron core column (3), and a small amount of magnetic flux passes through the middle iron core column (2), so that the current of the secondary coil L2 of the current transformer cannot exceed 120 percent of the rated current, and secondary equipment can be quickly protected.