The invention discloses an avermectin suspension and a preparation method thereof. Each 100 mL of suspension comprises the following components by weight: 1 to 3 grams of avermectin, 10 to 25 grams of absolute ethanol, 15 to 25 grams of polyethylene glycol, 0.6 to 1.3 grams of sodium carboxymethylcellulose, 0.5 to 0.7 gram of gelatin, 1 gram of tween 80, 0.5 gram of sodium benzoate, and the balance being injection water. The avermectin suspension is prepared by compounding avermectin, absolute ethanol, polyethylene glycol, sodium carboxymethylcellulose, gelatin, tween 80, and sodium benzoate, and the components mentioned above cooperate with each other to generate a synergetic effect. The provided suspension solves the problem that avermectin is hard to dissolve, can be rapidly absorbed by the gastrointestinal tracts, is completely absorbed in human body, has a high bio-utilization degree and large divergence, improves the sustained releasing and long acting effect of active components, has a rapid effect and radical curative effect on nematodosis, mite diseases, parasitic insect diseases of poultry and livestock, does not generate any drug residue, and is easy to promote and use in clinic.