Abstract: The flow experiment of wide,shullow and steopflume in the paper indicates that the resistance loss of shallow supercritical flow in the steep channel is more than that of the general open flow.The author analyzes the flow momentum distribution in wide and steep channel,and finds that when the ratio B/h< 40 and the discharge is larger(h_k> 1.04 m),the flow momentum lateral distribution at the end of steep channel presents a saddle profile which has stronger stability,but when the ratio B/h > 40 and the discharge is smaller (h_k < 1.04 m),the momentum lateral distribution presents a elliptical profile which has weak stability and can't restrain the boundary disturbance Based on intervenient method,an new adjusting work is done through the submerged triangle wing.It can effect ively restrain the progressive minor disturbance,named Domino effect and get satisfied effect.The author further discusses the controlling mechanism and the main factors,and obtains some designable principle and the dimensionless geometric factor k of submerged triangle wing for engineering.