The invention discloses an LLC resonance type three-port DC-DC converter and a control method thereof. The converter is composed of a primary side circuit, a secondary side circuit, a transformer and LLC resonant network. The primary side circuit is composed of a full-bridge unit integrating two paths of two-way buck-boost circuits connected in parallel in a staggered mode. The secondary side circuit is composed of a rectifier circuit. The transformer and LLC resonant network is composed of a high-frequency transformer, a resonant inductor Lr, an excitation inductor Lm and a resonant capacitor Cr. By adjusting the duty ratios and frequencies of power switch tubes of the primary side circuit, two-way energy transmission and output one-way energy transmission between two ports of the primary side can be effectively controlled at the same time. According to the converter and the method, a non-isolation type two-way buck-boost converter is integrated with an isolation type full-bridge LLC resonant converter, so that multiplexing of the primary side switch tubes is achieved, the number of the switch tubes is reduced, cost is reduced, and power density and reliability are improved. The converter is suitable for renewable energy source power generation, hybrid electric vehicles, fuel cell vehicles, hybrid energy storage systems and other systems.