The four-switch buck-boost converter has the advantage of multi-mode operation, which is suitable for a wide range of voltage regulation. To solve the problem of multi-mode efficiency reduction and multi-mode control, a loop-switch selective control strategy is proposed. Firstly, the Boost-T and Buck-T modes are introduced into the dead zone of the converter to form a four-mode control, which effectively eliminates the influence of the dead zone on the traditional two-mode control. Secondly, the switching boundary in the intermediate mode is optimized and the frequency conversion control in a small range is utilized to address the problem of reducing the efficiency of the converter after the introduction of the intermediate mode. Then, to solve the multi-mode control problem, a switchselective control strategy with input voltage feedforward is designed by exploring the law of the conjugate pole distribution of the system with the model parameters. Finally, an experimental prototype based on GaN is fabricated. Experimental results show that the output voltage ripples within 2. 5 V when the system load bursts, the output voltage ripples within 1 V when the mode is switched, and the maximum operating efficiency in the intermediate mode reaches 96. 3% when the load is full