With the improvement of the ecological environment, bird activities have become more frequent, posing a serious threat to the safe operation of transmission lines. In particular, bird droppings flashover accidents have become one of the important issues affecting the reliability of transmission lines. This paper proposes protective measures using insulating grading rings with different materials to deal with flashover failures caused by bird droppings after installing grading rings on composite insulators of 110 kV transmission lines. First, the influence of grading rings coated with different insulating media (plastic, polyethylene, silicone rubber) on the electric field and potential distribution of composite insulators was analyzed through finite element simulation. It was found that the insulating coating can effectively improve the electric field distribution and reduce the electric field intensity. Secondly, a guano channel flashover test platform was built for testing. The results showed that plastic, polyethylene and silicone rubber insulated grading rings increased the average breakdown voltage by approximately 5.2, 22.1 and 30%, respectively, effectively reducing the probability of guano flashover failures. This study provides an effective solution for improving the safety of transmission lines and has important engineering application value.