Co-Ni coated ZrO2 composite powder was prepared by an optimized ultrasonic electroless plating process to obtain good microwave absorption properties in GHz region. Aggradation mechanism of electroless Co-Ni alloy was analyzed and the principal influencing factors on the depositing rate were investigated by weighting-in-powder. The metallized powder was characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and vector network analyzer. Results showed that ultrafine ZrO2 powder pretreated with sensitization and activation were homogeneously deposited with Co-Ni coating at 358K and pH value of 9, immerged in the optimal plating bath using NaH2PO2 as reductant. The Co-Ni coating deposited in the alkaline plating bath had the depositing rate of above 6µm/h and the average weight ratio of 5.5 for Co/Ni. The new metallized powder was endowed high microwave absorbing properties; the maximum reflection loss reaches to -23dB at the frequency of 9.40 GHz.