Even- and odd-mode guided-wave characteristics of periodically nonuniform coupled microstrip lines (PNCML) are thoroughly investigated in terms of the two sets of per-unit-length transmission parameters, i.e., characteristic impedance and phase constant. By executing the short-open calibration (SOC) procedure in the method-of-moments platform, the two-port matrices of the PNCML with finite unit cells are numerically deembedded via two sets of SOC standards so as to explicitly derive the effective per-unit-length parameters. After our investigation on the behaviors of numerical convergence, extensive results are derived to demonstrate the frequency- and periodicity-dependent per-unit-length parameters of the three types of PNCML against those of the uniform coupled microstrip line. In final, the -parameters of a PNCML circuit are directly simulated via extracted per-unit-length parameters and they are validated in magnitude and phase by those from the Momentum simulator.