Aiming at the problem of electromagnetic interference in the shielded cables of high-speed railway. On the basis of the analytical model of single-shielded transfer impedance. Considering the effect of the double- shielded on the DC impedance and small-hole inductance of the shielded layer, an analytical optimization model is proposed for the shielded cables of high-speed railway. Combined with the theory of transmission line and shielding efficiency, the quantitative relationship between shielding efficiency and transfer impedance is proposed, and the theoretical mathematical model of core wire subjected to conduction interference is given. Finally, the shielded cable of high-speed railway is taken as the research object for modeling and simulation, in order to analyze the disturbance situation of the cable. Comparing the simulation value and the calculated value, which verifies the correctness of the model. The error rate of the optimization model is less than 10%, which verifies the effectiveness of the model. The disturbance mechanism of shielded cable of high-speed railway is revealed.