Chitosan was chosen as wall material to prepare the Na2SeO₃-loading microspheres with emulsion-crosslink method. Then, the microspheres’ appearance, drug loading capacity, encapsulation efficiency and its sustained-release property were chosen as evaluation criteria to optimize the process condition through the single factor experiments and the orthogonal tests. In addition to this, the structure of the microspheres was characterized preliminarily by the scanning electron microscopy (SEM), infrared spectroscopy (IR), atomic fluorescence, thermogravimetric analysis (TG), and its sustained-release property were researched in vitro under the circumstance of the simulated body fluid (SBF) which was prepared by ourselves. The best process condition to prepare the microspheres shown by the experimental results were as follow: the temperature was 65 ℃, the concentration of chitosan and sodium selenite was 3% and 0.8%, the dosage of crosslinking agent was 15%. Under such environment, the appearance of microspheres was pretty good, its encapsulation efficiency and drug-loading rate was 65.89% and 5.05% respectively and the average particle size was about 10 μm. The sustained-release rate of microspheres became stabilized after releasing for 482 h and its valid sustained-release time could last for 35 d. This experiment was expected to provide a new way to supply Se reasonably for the Se-shortage population.