The better the magnetic properties of the transformer core, the measurement error is smaller, the higher the accuracy. Require low ampere turns ratio small, cold rolled silicon steel reach the measurement accuracy, the permalloy core due to low saturation magnetic flux density and high cost because of the use of very constrained. Nano-crystalline cores are getting wider usage for the 0.2，0.2s, 0.1 accuracy grade precious current transformers because of its high permeability, high magnetization and lower cosl in Ihc field of power supply systems, power energy measurement and controlling systems, dynamical system, relay protection, etc.