Carbon fiber and silicon carbide fiber have been widely used in stealth technology,which are two main kinds of fibers to reinforce radar absorbing materials.Preparatibn methods and microwave permittivity and permeability of radar absorbing carbon fiber and silicon carbide fiber are discussed.Carbon fiber with good radar absorbing can be prepiared by decreasing its heat treatment temperature,changing its cross section shape and size,modifying outer surface and doping other elements into the carbon fiber.Silicon carbide fiber with radar absorbing can be prepared by increasing the heat treatment temperature,modifying fiber surface and doping other elements into fiber.