The invention discloses a spring yield type energy dissipator for a slope flexible protection system and a design method. The energy dissipator comprises spring steel, a rotating shaft, a pin shaft, aC-shaped clamp and an arc-shaped lug plate. The spring steel is tightly wound on the rotating shaft, the end, provided with a hole, of the spring steel extends out for a certain distance in the tangential direction of the rotating shaft and is connected with a supporting rope of the flexible protection system through the hole, and the other end of the spring steel is welded to the rotating shaft.The pin shaft is sleeved with the rotating shaft, a small gap is reserved, the pin shaft is connected with upper and lower clamp flange plates of the C-shaped clamp through bolts, the arc-shaped lugplate is welded to a C-shaped clamp web, and a lug plate reserved hole is connected with another supporting rope of the flexible protection system. When the flexible protection system is impacted, thespring steel connected with the corresponding supporting rope is pulled and rotated around the rotating shaft, the spring steel is changed into a straightened state from a bent state, and energy is dissipated through plastic deformation of the spring steel. After impact, the spring steel can be coiled into a spring shape around the rotating shaft from the straightened state for repeated use. Theenergy dissipator is reasonable in structural design, clear in energy dissipation mechanism, high in energy dissipation capability, convenient to disassemble, assemble and maintain, suitable for narrow space installation and capable of being repeatedly used.