The beach-bar reservoir has become an important exploration target in China, but its depositional mechanism and controlling factors have not yet been fully modeled. They have become an inhibitory factor for the exploration and development of beach-bar reservoirs. The depositional mechanism of beach-bars and their controlling factors have been studied by means of a flume experiment including seven runs under controlled boundary conditions which were the water level(Run 1, Run 2 and Run 3), wave parameters(Run 1, Run 4 and Run 5) and initial slope(Run 1, Run 6 and Run 7). The experiment revealed that the development of beach-bar was controlled by water level, wave parameters and initial slope. The deposited locations of distal bar and nearshore bar were controlled by the water level. Two beach-bars were migrated downward when the water level falls(Run 1, Run 2 and Run 3). The width and thickness of distal bar and nearshore bar were controlled by wave parameters, especially the wave height. They increased with the scale of wave. But, the maximum thickness is limited by the water level(Run 1, Run 4 and Run 5). The distance between distal bar and nearshore bar was controlled by the initial slope. It became shorter with the steeper slope. Distal bar and nearshore bar changed into one bar when the initial gradient was greater than 1/20(Run 1, Run 6 and Run 7). The results suggest formative mechanism and controlling factors related to beach-bars. The beach-bar reservoir has become an important exploration target in China, but its depositional mechanism and controlling factors have not yet been fully modeled. They have become an inhibitory factor for the exploration and development of beach-bar reservoirs. The depositional mechanism of beach -bars and their controlling factors have been studied by means of a flume experiment including seven runs under controlled boundary conditions which were the water level (Run 1, Run 2 and Run 3), wave parameters (Run 1, Run 4 and Run 5) and the initial slope (Run 1, Run 6 and Run 7). The experiment revealed that the development of beach-bar was controlled by water level, wave parameters and initial slope. The deposited locations of distal bar and nearshore bar were controlled by the water level. Two beach-bars were migrated downward when the water level falls (Run 1, Run 2 and Run 3). The width and thickness of distal bar and nearshore bar were controlled by wave parameters, especially the wave heigh They increase with the scale of the wave. But, the maximum thickness is limited by the water level (Run 1, Run 4 and Run 5). The distance between distal bar and nearshore bar was controlled by the initial slope. with the steeper slope. Distal bar and nearshore bar changed into one bar when the initial gradient was greater than 1/20 (Run 1, Run 6 and Run 7). The results suggest formative mechanism and controlling factors related to beach-bars.