Ferrite and silicon carbide with excellent electromagnetic microwave absorption performance were used to modify magnesium oxysulfide cement foam plate. The influence of different doping amount of ferrite and silicon carbide on the microwave absorbing perfermance of modified magnesium oxysulfate cement was studied. The effect mechanism was analyzed by X-ray diffraction and scanning electron microscopy. The results show that in the target frequency band of 3.95-18.00 GHz， 5% silicon carbide can make the material reach the lowest reflectivity， which is -15.9 dB at 8.40 GHz. 15% ferrite can make the material reach the lowest reflectivity， which is -17.3 dB at 7.04 GHz. The modified magnesium oxysulfide cement has good microwave absorbing perfermance when ferrite and silicon carbide were added to the magnesium oxysulfide cement matrix at a certain proportion.