As a new non-contact sensor for measuring lightning current, PCB (Printed Circuit Board) differential ring can realize the digital cabling and automatic production so that many negative factors of traditional differential ring are overcome. For the reason that the measurement sensitivity of single layer PCB differential ring is not high, the measurement principle of multilayer PCB differential ring is analyzed in this paper, and the related formulas are derived. The equivalent circuit of the multilayer PCB differential ring is given, along with the formula and the derivation of the capacitance and inductance in the equivalent circuit. Finally, the influence of the structural parameters of the multilayer PCB differential ring on the measurement performance is simulated by MATLAB software. The simulation results show that the measurement sensitivity of multilayer PCB differential rings and differential ring layers has a linear relationship. The more the layer number is, the higher the sensitivity; In addition, the more layers PCB differential ring, the smaller the distance between the layers, the smaller the distance between the shielding shell, the smaller the measurement bandwidth. The research results of this paper lay a theoretical foundation for the practicality development of the multilayer PCB differential loop and lightning current monitoring system.