As electronic technology advances towards higher integration and miniaturization, three-dimensional circuit layouts have become increasingly prevalent, making the effective transmission of millimeter-wave signals between the surface and internal circuits particularly critical. This study presents a novel design for an ultra-wideband, low-loss vertical interconnect structure transitioning from a stripline to a Grounded Coplanar Waveguide(GCPW), aimimg at addressing signal reflection and radiation issues caused by parasitic inductance and capacitance in interconnect structures. Through the analysis of an equivalent circuit model and preliminary parameter design, combined with optimization using three-dimensional field simulation, the final design parameters were determined. The interconnect structure employs a 0.2 mm diameter via for connection and features an isolation ring with a mere 0.8 mm diameter, ensuring the simplicity and ease of fabrication of the structure. Simulation results indicate that the design achieves broadband coverage from DC to 80 GHz, with S11 less than -13 dB and S21 greater than -0.4 dB, demonstrating excellent performance. To interface with the testing system, a test board was designed to convert to a coaxial connector, extending the operating frequency to 40 GHz. Actual test results show that, within the DC to 40 GHz range, return loss is less than 11 dB and insertion loss is less than 0.4 dB, further verifying the effectiveness and practicality of the design.