Abstract: A flexible variable-mode wide gain range control strategy was proposed for the full-bridge LLC converter. This article discussed the state analysis model of full bridge LLC, sub-mode control principles, and established a digital-aided design platform. These theories and tools laid the foundation for the follow-up works. Aiming at the deficiencies of the existing full-bridge LLC converters of independent sub-mode logic and limited overall gain range, a smooth and flexible variable-mode control strategy combining full-bridge frequency control, asymmetric phase shift control and DPWM control was proposed. The working characteristics of each sub-mode, the technical issues and design points, such as the matching of the working machine and the state transition process, were explained in detail. The prototype experiment proves that the proposed method allows the full-bridge LLC converter to achieve an extremely wide gain range, and ensure the zero-voltage switching and hence high operating efficiency in the full operating range.