The invention relates to a current mutual inductor field detecting device for protection, comprises combined type voltage proportionality standard consists of HP1 voltage proportionality standard witha booster and HP2 voltage proportionality standard, an HP3 current mutual inductor and an HEW mutual inductor checking meter, so as to be capable of detecting the current mutual inductor for protection. The device can detect the specific value error and the phase error of 5P level and 10 level current mutual inductors for protection under rated load and electric current, composite error under anaccuracy limit factor ALF, or the composite error of 1 level to 0.2 level field current mutual inductors under the rated load and security factor FS, and the complete VA characteristic of the mutual inductor, and can draw a complete VA characteristic curve, a composite error curve and a 10% and 5% multiple curve by communicating with the compute.