The invention discloses a precisely identifying method for geometric stiffness of a section of a cable strut. The precisely indentifying method is a method for precisely indentifying the geometric stiffness of the section of the cable strut by computing inertia moment of a circular section of a steel wire based on hierarchy and sequentially comprises the following steps of step 1, carrying out equilateral hexagon hierarchy on the section of the cable strut, namely dividing the section of the cable strut into n equilateral hexagons from interior to exterior, acquiring basic parameter information of the section of the cable strut, including the number of steel wires in the cable strut, the axial force born by the steel wires, the elasticity modulus of steel wire material and the section area of each steel wire; step 2, computing the section inertia moment I' of the section of the cable strut without bearing the axial force through a formula I'=Cnr<4>; step 3, computing the section inertia moment I of the section of the cable strut bearing the axial force through the formulas I=IrfI'= I'(1+epsilon') and epsilon'=-vF/EA; and step 4, multiplying the section inertia moment I obtained by the step 3 by the elasticity modulus of the steel wire material to obtain the geometric stiffness of the section of the cable strut. Through the precisely identifying method disclosed by the invention, the result has high precision and small error.