The existence of homoclinic orbits to saddle-focus

In this paper, an error of Zhou [Chaos Soliton. Fract. 19 (2004) 985] is pointed out through an example. And the improvement for the method of criterion to the existence of homoclinic to saddle-focus is given. Using this method, we can solve this example correctly, and easily get nonexistence of horseshoe chaos in meaning of S̆il'nikov.