A radial gate opening degree calculation method comprises the following steps that step S1, a circle O2 is made with the fulcrum as the center and the length of a lifting rope as the radius R2; step S2, a circle O1 is made with the supporting hinge as the center and the length of the supporting arm as the radius R1; step S3, a rectangular plane coordinate system Oxy is established with the supporting hinge as the original point; step S4, the circle center coordinate of O1 is set as (0, 0), the circle center coordinate of O2 is set as (x0, y0), x0 is the horizontal distance from the fulcrum tothe supporting hinge, and y0 is the vertical distance from the fulcrum to the supporting hinge; step S5, the circle O1 and the circle O2 are intersected at two points p and q, wherein the position where the point p is located is a lifting point; step S6, the angle value of the point p on the circle O1 is set to be alfa, wherein the angle pos is beta; step S7, the distance between the supporting hinge and the s point at the bottom of the arc-shaped gate leaf is set to be R3; step S8: R1, R2, R3, x0 and y0 can be measured by a tape; and step S9, solving an s point coordinate value. Real-time, rapid, accurate and convenient data calculation is adopted, and the data measurement difficulty is reduced as much as possible.