Abstract: Coaxially-shielded through-silicon-via with mixed dielectric layer (MD CSTSV) has showed great application prospect in the field of high density RF packaging due to its excellent electrical properties, simple fabrication process and low cost. In this paper, an equivalent circuit model of MD CSTSV was established based on the theory of multi-conductor transmission line and the calculation formulas for complex capacitance of annular dielectric layer with introduced scale factor λ, obtaining RLGC electrical parameters of the structure per unit length. The results show that in the frequency range of 0.1~40 GHz, the S-parameter results calculated through the equivalent circuit model of MD CSTSV are consistent well with those obtained from HFSS full wave simulation, presenting less than 7% maximum error. All the results show that the extracted per unit length RLGC electrical parameters of MD CSTSV and the corresponding equivalent circuit model can be used to accurately simulate the signal transmission performance of MD CSTSV.