Abstract: The flood with hyperconcentration in the midstream Yellow River frequently causes the bottom tearing scouring.Based on the analysis of the bottom tearing scouring,this paper sets up the physical mode about the bottom tearing scouring and derives the mechanics equation of the bottom tearing scouring and the critical condition of the water and sediment,and the results of calculation agrees with the measured records.Based on the analysis of the equation and condition,the starting current velocity formula about the pill sediment is further pnwed.The twa formulas derived possess important theoretical value to the research of river floor variation and sediments starting caused by the flood with hyperconcentration.