Wang, Y.G. JACoW Publishing Geneva, Switzerland Carbon material has a high reflectivity on the synchrotron radiation. It might be introduced into the accelerator to eliminate heat load in the cryogenic section induced by the high synchrotron radition. Coating carbon film on the accelerator wall has been confirmed a very effective method to mitigate the electron cloud. Here we will analyze the relatonship between the reflectivity and the secondary electron yield.