Lightning over-voltages are the important reasons for losses in communication port,which make it necessary and urgent to study into the lightning protection of communication port.According to the protection characteristics of gas discharge tube and transient voltage suppressor,the decoupling components are selected carefully to achieve the rational energy correspondence between multi-level SPD.Besides that,optical design is also considered to design protective circuit of RS-232 port.Finally,in order to verify the design scheme,the lightning impact platform called LST-6 kV/3 kA and ICGS and function generator called DF1641C are employed for the experiments.The experiments show that bearing capacity of lightning over-voltage of communication port RS-232 has been greatly improved and will not produce insertion loss to original circuit by adding the protection circuit.