The bed in the edge of soft mattress is easy to be scoured by unfavorable flow.When the scouring depth exceeds the deformation capacity of soft mattress,the edge of it sometimes appears deformation failure.The paper analyzes the influential factors of the deformation failure of soft mattress,which includes the flow conditions,bed composition,as well as the structure and width of soft mattress.The failure mechanism of soft mattress is also studied and corresponding counter measures are proposed.It indicates that a permeable frame of certain density can reduce the turbulent intensity near the bottom boundary flow and the bed scouring in the edge of soft mattress,which can maintain the safety of soft mattress and spur dike.