Compound diclazuril nanoemulsion was prepared and its quality was evaluated. The preparation of compound diclazuril nanoemulsion was optimized by studying the pseudoternary phase diagrams. Compound diclazuril nanoemulsion was prepared, its shape and particle size distribution were detected by TEM and Nicom p388/Zeta PALS Particle Sizing System and its stability was verified by high speed centrifuge test and long term storage test. The optimum preparation was w(diclazuril)=5%, w(Vitamin K3)=10%, w(Tween-80)=30%, w(ethanol)=5%, w(ethyl acetate)=3.9%, w(Dimethylformamide)=2.5%, w(distilled water)=43.6%. The shape of compound diclazuril nanoemulsion was spherical, with mean diameter of 14.0 nm and polydispersity index was 0.064. The high speed centrifuge test and long term storage test showed that it was still clear, lucent and uniform. The preparation procedure of compound diclazuril nanoemulsion is simple and the stability is good. It is expected to be applicable to the veterinarian clinic.