The performance of the medium-frequency inverter is highly related to the active damping of the filter resonance. Due to the presence of the digital control delay, the system stability analysis is more accurate in the z-domain. Therefore, the accurate discrete model is the prerequisite to guide the implementation of the control strategy. The modified input matrix is elaborated for the derivation of the discrete state-space model, which avoids the conventional complicated algebraic calculation of the residues of all poles. The proposed generalized discretized method of state-space model is revealed to be feasible for the medium-frequency system with the arbitrary digital control delay, which undoubtedly provides an alternative way for the analysis of the complicated system, e.g., the multiple-sampling or reduced control delay. The frequency-sweeping method is finally used for verifying the correctness of the proposed discrete state-space model.