Network analyzer was connected with rectangular resonant cavity to build up a perturbation measurement system for electro-magnetic parameters of materials.Based on perturbation theory,the measurement equations for the complex-permittivity and permeability of small volume materials loaded into sample holders for measurement were obtained.The electro-magnetic parameters of a novel radar absorbing material,carbon foams,were measured.It shows that the εr′ and μr″ value of carbon foams increase gradually with the increase of electric conductivity,while the εr″value increases firstly and then decreases.Carbon foams are characterized by small permittivity,large electric loss and extrinsical magnetic loss.The unique electro-magnetic loss characteristics of carbon foams make it possible to be used as structural radar absorbing materials with wide absorbing bandwidth at elevated temperatures.