Abstract: Nano-sized Fe<SUB>3</SUB>O<SUB>4</SUB> is a kind of important multifunctional magnetic material.The key influencing factors of synthesizing nano-sized magnetic Fe<SUB>3</SUB>O<SUB>4</SUB> particles by hydrolytic method include curing temperature,amount-of-substance ratio of Fe<SUP>2+</SUP> to Fe<SUP>3+</SUP>,and pH of titrating termination.The orthogonal experiment results showed:under these conditions,amount-of-substance ratio of Fe<SUP>2+</SUP> to Fe<SUP>3+&nbsp;</SUP> was 1∶1.75,constant curing temperature was 80 ℃,and pH of termination was 11.,nano-sized magnetic Fe<SUB>3</SUB>O<SUB>4</SUB> particles with size distribution under 0.1 μm and mass fraction up to 95.53% was prepared.The prepared sample was characterized by X-ray diffraction (XRD),transmission electron microscope (TEM),and vibrating sample magnetometer (VSM) respectively,the analysis results showed that the prepared nano-sized Fe<SUB>3</SUB>O<SUB>4</SUB> particles were single-phase cubic structure with high purity,superparamagnetic and average grain size of 56 nm.