By analyzing application of electro-magnetic ecotypic environmental material, multicrystalloid ferrite powder were chosen as electro-magnetic wave absorber, which possesses good properties of electro-magnetic loss. A site experiment has been carried out in a power switch room by plastering the wave absorbing mortar in one residential project. The wave absorbing mortar has a good workability with satisfied finish, and has an notable attenuation of electromagnetic energy within the testing space at the range of 1-50 MHz.