Abstract: An integrated Buck-Boost CLLC converter used for wide input voltage and in common input-output environment has been researched. Through the integration of Buck-Boost with the primary side of CLLC, high DC gain can be obtained by bus capacitor on the secondary side superimposing on that primary side. The converter is integrated with the half-bridge CLLC via Buck-Boost and synchronously controlled by fixed-frequency PWM strategy, and the MOSFET can be soft switching in wide input voltage range and load conditions that use for improve power density. This paper introduces the topology of the IBBCLLC and the operation mode, demonstrates that turns ratio of n₁: n₂= 1: 1 can produce high DC gain, the size of the transformer becomes smaller and the current stress of the transformer primary side reduces. In addition, this paper provides the soft switching conditions by analyzing the effect on the soft switching performance from Buck-Boost inductor. In conclusion, a prototype with 20~80 V low voltage side, 100~400 V high voltage side and 600 W output power is established, which proves the theoretical analysis is correct.