The four-switch buck-boost converter has the advantage of multi-mode operation and is suitable for a wide range of voltage regulation. In order 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 in 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 adopted to solve the problem of reducing the efficiency of the converter after the introduction of the intermediate mode. Then, in order to solve the multi-mode control problem, a switch-selective control strategy with input voltage feedforward was designed by exploring the law of the conjugate pole distribution of the system with the model parameters. Finally, an experimental prototype based on GaN was fabricated, and the 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.