In the application environment of medium-voltage distribution lines and their stable currents, in response to the limitations of traditional voltage and current separate measurement, the internal safety of insulators after the integration of primary and secondary systems, the difficulty in determining the voltage measurement gain, and the anti-interference ability of TMR current measurement. A voltage-current integrated sensor based on electric field coupling and TMR magnetic sensing is proposed for insulators. On the one hand, a simulation-based optimization method is proposed for the structural parameters of the voltage sensing embedded within the insulator. The structural rationality is verified through simulations focusing on electric field distribution and insulation strength. Under the geometric constraints of the insulator model, the optimal structural parameters are obtained to achieve uniform induced electric fields, a well-defined transfer function, and minimized partial discharge after the voltage sensing unit is integrated into the insulator. This ensures the safety of the insulator and improving the voltage measurement accuracy. On the other hand, an open-loop two-stage magnetic ring current sensor based on TMR is proposed, which is placed at the top of the insulator. The dimensional parameters of the magnetic rings are designed through simulation analysis of the magnetic sensitivity characteristics, thereby improving the sensitivity, anti-interference capability, and magnetic field uniformity at the sensing point, enabling accurate measurement ofa wide-range current signal in open-loop conditions. An integrated sensing structure and system are ultimately designed for multiple experiments. Under power frequency conditions, the maximum relative error of the effective voltage measurement from 1 to 14 kV is 1.49%, and 1.41% under 10 kV input a with interference. For current measurements ranging from 1 to 120 A, the error under oscilloscope acquisition for signals above 2 A is within 1.2%, and -1.129% relative error under 20 A input with interference. Experimental results within the test range demonstrate that the proposed voltage-current integrated sensor offers certain anti-interference ability, accuracy, stability, and dynamic range.