Matching networks for ultra-high frequency chips are susceptible, and accurate extraction of passive devices parameters is essential. For on-chip transmission lines, the authors present a precise method of extracting transmission line propagation constant from two transmission line measurement structures with different lengths. After obtaining the propagation constant based on this method, to get the transmission line’s characteristic impedance, this paper conducts a Y-Z model analysis of the signal pad and gives mathematical expressions. This approximation method can obtain the characteristic impedance of the transmission line without solving the signal pad’s model parameters. The propagation constant and characteristic impedance derived from the methods proposed are compared with the corresponding electromagnetic simulation results, achieving fairly good agreement from 250 MHz to 110 GHz.