Abstract: The existing measurement current transformers are easy to be saturated, and the protection transformers and the measurement transformers are generally installed independently, resulting in large volume and high cost. In order to protect the integrated current sensor, it is proposed to make a ring-shaped double-iron core design with ultra-microcrystalline and notched silicon steel sheet materials, and the windings are evenly wound on the double-iron core. In this paper, a magnetic circuit model of double-core skeleton is established, and the error of the transformer under different skeleton ratios is analyzed. Combined with the actual production and the size of the iron core, the optimal skeleton ratio is determined. Finally, it is verified through experiments that the sensor can not only ensure 0.2-level accuracy under the rated current, but also ensure that it is not saturated under 20 times the rated current, which can realize the integration of measurement and protection functions. The integrated design can effectively save space and cost.