The multipactor effect is a resonant vacuum electron discharge that can occur in microwave and millimeter-wave subsystems,such as filters,multiplexers,and radio-frequency satellite payloads.In a high-power microwave device,multipator discharge can cause the device to break down,and thus degrading its performance.Fortunately,the multipactor effect can be mitigated by reducing the secondary electron yield (SEY) of the material which a microwave device is made from.Therefore,how to reduce the SEY of material is an important matter.In view of this problem,a new method to reduce the SEY is presented in this paper.This method is based on the fact that when aluminum sheet is treated with anodizing,many porous structures with high height-to-width ratios can be formed on the surface of sheet.These porous structures are conducive to reducing SEY.However,the alumina film covers these porous structures.Because alumina has poor performance in conductivity,the loss of high-power microwave device will increase if the microwave device is anodized.In consequence,the performances of the microwave device will deteriorate.In order to avoid this problem, silver film is chosen,and is electroplated on the anodized aluminum sheet.Although silver film is electroplated on the aluminum sheet,there are still many porous structures on the surface.In order to validate the method in this paper, some aluminum samples are anodized.And then,the SEYs of these samples are obtained by the SEY measurement system.The results show that this method is efficient for reducing the SEY.Compared with the non-anodized sample, the uncleaned sample on whose surface there exists the adsorption or contamination shows that the value of the first energy crossing point of the measured curve of emission coefficient of secondary electrons,E1,increases from 45 eV to 77 eV,and the maximum value of SEY (SEYmax) decreases from 2.68 to 1.52;when the samples are all cleaned (in order to obtain ideal surface by wiping off adsorption or contamination),the value of E1 increases from 40 eV to 211 eV, and the value of SEYmax decreases from 2.55 to 1.36.Furthermore,the multipactor threshold of an X-band impedance transformer is simulated with using these SEY data to validate this method.And it is concluded that compared with the threshold of the original design,the multipactor threshold of the impedance transformer which is treated with the method increases from 7000 W to 125000 W.Therefore,it can be seen that the method presented in this paper is helpful in solving the problem of the multipactor in high-power microwave device for space.Meanwhile,as a usual method,the method can also be used to push forward the researches of vacuum electron devices and accelerators.