The invention relates to an automatic calibrating device for a large current transformer. The automatic calibrating device comprises a voltage regulator, a large current generator, a standard current transformer, a switch controller, a secondary wiring control module, a current transformer calibrator, a control computer and a current load box. The automatic calibrating device and method for a large current transformer realize integration of large current transformer calibrating equipment. A primary loop and a secondary loop allow automatic wiring, and automatic calibrating of current transformers to be tested can be done. Safety of calibrating work and calibrating efficiency for current transformers are improved.