Whereas the bottom protection of spur dike can compress the general ineffective scouring range to increase the effective action efficiency of spur dike，a method for determining the bottom protection width of spur dike based on the waterway scour efficiency has been proposed. The main conclusions are drawn as follows through theoretical analysis，numerical simulation，and physical model test research：the effective action efficiency coefficient of the spur dike is the ratio of the increase in the single-width flow of the movable bed waterway to the increase in the single-width flow of the fixed bed waterway. Calculation formula for the effective scouring efficiency of the spur dike is established，which can be used to calculate the bottom protection width of the spur dike. The formula shows that the effective scouring efficiency of the spur dike is constant；when the bottom protection is from the spur dike root to the edge of the waterway to form a fixed bed condition，the effective scouring efficiency of the spur dike can reach 100%. By this method，the width of the bottom protection can be reasonably determined. Therefore the general invalid scouring range of the spur dike head can be reduced，and the effective scouring efficiency of the spur dike on the waterway can be increased. In this way，the improvement effect of the navigation channel after the engineering is better.