The invention relates to a method for improving the flow regime of a high velocity flow of a sharp bend section in a free-flow tunnel, and belongs to engineering methods for improving the flow regime of the high velocity flow of the sharp bend section in the free-flow tunnel. The method comprises the steps of arranging a bend stilling pool inlet slope section on a straight-line section of the tunnel, and calculating the pool depth of a stilling pool through a derived bend stilling pool computing method; enabling the gradient of the bend stilling pool inlet slope to be the same as the injection angle of the flow, arranging stairs at the lower part of the inlet slope, and enabling the width of the bend stilling pool to be the same as the width of the tunnel body; arranging a bend stilling pool outlet slope section on a downstream straight-line section, arranging a stair-type slope at the stilling pool outlet slope section, and calculating the total length of the stilling pool, wherein the stair height is 1/2 of the pool depth of the stilling pool optimally. According to the method, the flow regime of the high velocity flow of the sharp bend section in the free-flow tunnel is improved, and the flow regime of the high velocity flows of various bends or the flow regime of middle and low velocity flows of sharp bend sections in the free-flow tunnel can be improved the same, so that the curve layout of the free-flow tunnel is more flexible, and the method has quite good practicability and application prospect.