In order to improve the loading speed of valve controlled asymmetrical cylinder in aircraft structure fatigue test, unidirectional loading method was presented, and mathematical model was established. Loading performance indicators were analyzed and validated including loading speed, maximum overshoot and energy consumption. Unidirectional loading method is very important in engineering application with obvious advantages compared with the conventional loading of valve controlled asymmetrical cylinder, including higher loading speed, less overshoot, and lower energy consumption.