This paper proposes a generalized model based on the generalized state-space averaging model for dual-active-bridge (DAB) DC-DC converters. The proposed model is suitable for all modulation modes, and the model is general, and the model will not be different due to the change of the transmission power mode. The model uses the AC first-order component of the inductor current and the DC component of the capacitor voltage as state variables to establish the state equation. Based on the large-signal model, the small-signal model and the transfer function from the control variable to the output voltage are derived for the DAB converter. Finally, an experimental prototype of DAB converter is built, and small-signal analysis is carried out based on the simulation software and the experimental prototype. Comparing the proposed model with the reduced-order model, the proposed model is more matched with the experimental and simulation results than the reduced-order model, which verifies the accuracy of the model.