Avermectin microspheres were prepared with sodium alginate and chitosan as wall material using dropping method. The effects of the concentration of sodium alginate, chitosan, calcium chloride and the ration of the core-wall on the microsphere morphology, particle size, embedding rate were investigated. The properties of microspheres were characterized by SEM and FTIR, and the release properties and mechanism in soil were studied. The experiment results showed that the optimized preparation conditions are as follows: the concentration of sodium alginate, chitosan and calcium chloride were 3%, 0.6% and 5%, respectively. The ration of core-wall was 1:2. The prepared microspheres had good spherical shape and its average diameter is about 0.7 mm, the drug content and the encapsulation efficiency were 31.65% and 83.81%, respectively. FT-IR analysis displayed there was no chemical interaction between the core and wall material in addition to the hydrogen bonding. The avermectin release characteristics of microspheres was in accord with the Riger-Peppas model, and the release mechanism was Fick diffusion.