The invention relates to an open-close style current transformer, comprising a coil, a transformer iron core and a casing. The transformer iron core consists of two arc-shaped iron cores which can combined into a circle. A coil is winded on the big arc-shaped iron core and short circuiting rings are distributed on the small arc-shaped iron core. The magnetic field strength generated on the short circuiting ring can enhance magnetic-force line strength of an open-close point of the open-close style current transformer so as to overcome the problems that the output capability is low, the accuracy is low and the angle difference is large when in work.