The abstract is based on the principle of generating proportional standard errors in high-precision circuits, designs a magnetic shielding effectiveness testing device, and analyzes its shielding effectiveness from the materials, structures, layers, thickness, and combination methods of the shielding body. Based on the consistency between the two-dimensional finite element method and the magnetic circuit analysis method, the impact of different shielding schemes on its shielding effectiveness is quantitatively given through finite element simulation and magnetic shielding effectiveness testing. The shielding optimization plan for the current comparator in production and manufacturing is proposed. By simulating interference with external magnetic fields and testing the voltage change detected by the current comparator at the output of the winding, the shielding effectiveness is indirectly calculated through the change. Based on the research results of this project, a special multi-layer shielding design is adopted from the aspects of shielding materials, number of layers, and combination methods. A shielding scheme for the current comparator is proposed, and a high-precision current comparator is developed. The experiment proves that the error of the current comparator can reach 5 × 10–8, verifying the feasibility of the shielding scheme.