The parallel gap lightning protection device is beneficial to the existing lightning protection measures for overhead transmission line and has broad application prospects.The application investigation on parallel gap lightning protection device of composite insulators for the 110 kV overhead transmission line used in Dongguan Power Supply Bureau is presented in this article.A variety of parallel gap lightning protection devices are designed.The functions of its guiding lightning discharge,transferring frequency arc,homogenizing frequency electric field and protecting insulators and fittings are verified by tests.After optimization of the design to determine the electrical parameters and dimensions of the gap,the samples are developed and used in five 110 kV transmission lines.The operation situation of the parallel gap lightning protection of composite insulator for 110 kV line is introduced.