State trajectory prediction is applied to regulate the output voltage of buck-boost converters. A second-order switching surface is designed based on the predicting the output voltage after a hypothesized switching action，so the output system can reach the target operating point in one switching cycle. The proposed method， with the characteristics of fast dynamic response，simple stability criteria，and strong robustness against input disturbances and output load disturbances，is suitable for large-signal analysis，and can be applied to other nonlinear power converters.