In order to meet the needs of building a new type of power system under China's "dual-carbon" strategy, for the new energy grid-connected many problems affecting the accuracy of power metering, by analyzing the current transformer error and the amount of influence, we propose the design of multiple micro air gap composite cores, which are designed through the equivalent circuit, the determination of the air gap, the selection of the core material and other aspects and verified by simulation. Tests on the designed HL(D)-500/5 current transformer show that its accuracy reaches 0.2SS level in the range of 0.1% to 200% In at the industrial frequency, and 0.2 level when superimposed with 10% DC component, which meets the metering requirements of the new type of electric power system in a wide dynamic range and with DC component.