Main transformers of high-power switching power supply, such as inverter, X-ray power supply, laser power supply, communication equipment power supply, high frequency induction heating power supply, and UPS. With the maturity of high frequency inversion technology, the inverter's advantages including small size, light weight and high efficiency are more obvious. As the heart of inversion welder, the main transformer has working frequency of over 20kHz, so the traditional core material silicon steel cannot meet operating requirements; The ferrite has low frequency loss, but ferrite core's volume and weight are large due to lower saturation magnetic induction value (Bs), besides, the ferrite has low Curie temperature, and poor heat stability. Fe-based -crystalline material has excellent integrated magnetic properties: Saturation magnetic induction is three times of ferrite, output power of the core with same volume is 2 times higher than ferrite, and the material has larger anti-overload capacity, and integrates advantages of silicon steel, permalloy and ferrite, namely high magnetic induction and permeability, low loss, and excellent temperature stability, so it becomes the best choice of inverter transformer core rapidly.