In this paper, a numerical short-open calibration (SOC) method is presented to numerically deembed the complex propagation constant of half-mode substrate integrated waveguide (HMSIW). After three distinctive equivalent circuit networks are described for SOC deembedding procedures, the propagation characteristics of HMSIW can be extracted. The numerical stability and convergence are illustrated. Two examples designed with the application of our method are given. An HMSIW leaky wave antenna is designed, fabricated, and measured. The radiation pattern calculated from the deembedded complex propagation constant is well verified by the simulated and measured ones. The scattering parameters of two classes of single microstrip-to-SIW transitions are extracted and they are used to validate the numerically deembedded complex propagation constant of SIW.