The rotary clamp spacer-damper is a new hardware. And because of its short time in application and the influence of style, amount and installation position, it is difficult to put forward a desirable evaluation method for its anti-galloping effect. With considering these factors, and in order to avoid complicated vector operation, the differential equations of conductor motion were derived from the Lagrange equation, when the conductor spacer-damper was covered by ice； and the time-responses of conductor galloping under the conditions of different kinds of spacers and different installation positions were calculated. Then, an evaluation method of anti-galloping effect was proposed based on the designing parameters of the conductor spacer-damper and the fuzzy mathematics theory. The analytic results show that the rotary clamp conductor spacer-damper has a better effect of anti-galloping. In addition, since the torsion angle of the sub-conductor also could affect the galloping prevention effect, therefore, an improved method of increasing the conductor torsion angle was put forward.