A dynamic differential geometry model of a hybrid underwater glider is established from the viewpoint of energy using the Riemannian differential geometry and affine connection. The model is used to analyze dynamics of the hybrid underwater glider system, including the hybrid driving systems, the posture adjustment systems, as well as the external force and torque. Numerical simulation is also conducted to analyze the saw tooth motion pattern in the vertical plane. The relationship between control inputs and characteristic motion parameters is obtained accordingly. Comparison between the simulation results and the experimental data recorded in the South China Sea shows a good agreement, verifying the validity of the proposed dynamic differential geometry model. This work provides guidance for dynamical behavior prediction and system design improvements for the hybrid underwater glider.