Cracks usually would appear on the surface of shed and housing of composite insulators due to aging or mechanical stress.The use of room temperature vulcanized silicone rubber（RTV）for repairing is a commonly used method.But there are few studies have been reported on coating thickness.In this paper

the high temperature vulcanized silicone rubber（HTV）is used as the basic material

while RTV is used to repairing cracks to simulate the surface of composite insulator coated by RTV.The effects of different RTV coating thickness on tensile strength

elongation at break

modulus of elasticity and hardness are investigated by means of tensile testing machine.It is found that the tensile properties of cracked specimens are lower than those without cracks due to stress concentration.Coated with RTV coating

the tensile properties of the material can play a certain role for repairing

and the greater thickness is

the more obvious repair effect turn out.But with the thickness increases

the hardness of double layer medium decreases

or the toughness of silicone rubber becomes larger.Thus

the local resistance of silicone rubber to the invasion of external objects decreases

which affects the mechanical properties of composite insulators.Therefore

RTV coating should not be too thick.