The invention discloses pet shampoo and a preparation method thereof. The pet shampoo is prepared by adding antioxidant, a surface active agent, dimethyl silicone oil, pH modifier, preservative, a thickening agent, conditioner and spice with natural pyrethrin as raw materials. The preparation method includes the steps of weighing all raw materials according to the ratio and formula and sequentially adding the raw materials and conducting even mixing and stirring to obtain the target product, wherein the temperature in the even mixing and stirring process is controlled between 10 DEG C and 35 DEG C. The pet shampoo is excellent in medicated effect, easy to degrade, friendly to the environment and safe for warm-blooded animals, has an ideal pet parasite killing effect, and has a nursing effect on hair of pets.