Abstract: To address the transformer DC bias caused by urban rail transit stray currents and improve the time-consuming and interference-prone traditional contact resistance test methods, a rapid test method based on broadband impedance spectroscopy and a four-terminal circuit is proposed. Based on dielectric polarization theory, a fractional-order complex impedance model of the contact interface is constructed by introducing a constant phase element to physically mitigate the influence of transient polarization effects on impedance measurement. The four-terminal sensing structure is adopted to reduce lead errors, and the Levenberg-Marquardt optimization algorithm is utilized to achieve rapid parameter inversion of contact resistance. Experimental validations show that the single test time is within 25 seconds, and the relative root mean square error under severe interference is 2.8%, effectively improving the test efficiency and anti-interference ability. Furthermore, the parameter inversion of various materials reflects the interface capacitance advantages of porous materials such as carbon fiber in high-frequency current dissipation. This method provides a practical engineering tool for the condition assessment of complex power grid grounding systems.