The invention discloses a design method of a guyed tower for ultrahigh voltage +/-800kV engineering. The method comprises the steps of drawing a clearance circle according to the design condition, producing the clearance circles for various design conditions and envelop curves of the clearance circles, and calculating the space between horizontal lines, space between vertical lines and distance to ground of guide lines; setting the space between two vertical columns and the positions of insulator string suspension points according to the size of the envelope curves of the clearance circles, the space between the horizontal lines and the space between the vertical lines of the guide lines, and creating a preliminary scheme of an iron tower; calculating the design conditions including heavy wind, ice covering, line breaking and installation, loads including operation overvoltage, thunder and lightning overvoltage and working conditions including electric work and the load combination through a nonlinear calculation module; adjusting the preliminary arrangement scheme of the iron tower according to the load and load combination; adjusting the specification of any rod without meeting the stressing condition; finally determining the space between the vertical columns, inclination angles of the main columns, the positions of the insulator suspension points, the positions of the guide line suspension points and the inclination of bracing wires as well as the specification of a component and joint design.