Abstract: Measurement method is very important in radom producing and researching.To our best knowledge,the usually measurement way of radom is antenna-radom system parameter method and IPD(insertion phase displacement) method.It's not quite convenient in engineering application.A new measurement way of radom-reflection coefficients method is presented here.Through measuring the phase of reflection coefficients of radom wall,the relative change of electrical thickness of radom wall can be known and the radom can be tested and repaired.Compared with other method,it use only one probe,so this method operate easily,the probe need not high positioning precision and can measure accurately.Especially,this method can be applied by the tip position of a complex radom easily and the theory of this method can be used in lossless measurement of dielectric material as well.