Y2O8/ZrO2 ultrafine powder was prepared by co-precipitation process using ZrOCl3·3H6O, Y(NO2)2·3H2O, concentrated ammonia, etc. as starting materials. The effects of ZrO2 seed dosage, precursor reaction temperature, reactant concentration, reaction system pH, dispersant dosage, aging temperature and heat treatment temperature on the synthesis of Y2O3/ZrO2 ultrafine powder were studied. The results show that the grain size of the powder prepared under experimental conditions is about 15 nm, and the secondary particle size is about 100 nm. The initial formation temperature of Y2O3/ZrO2 ultrafine powder was about 400 °C.