Experimental investigations were conducted on the process of surface erosion and channel network formation on the bare slope. This is the process of sediment yields on the river basin. Some experiments were conducted to clarify the process of the erosion by varying both the gradient of slope and the width of mouth at the downstream end. It was found that characteristics of channels were different among the experiments, such as length, width, branches and interruptions. As a result, it became clear that the steepness of slope affects the length of the channel network in longitudinal direction. The width of the mouth, on the other hand, affected the width and the pattern of channel network in lateral direction.