The invention discloses a preparation method of an aprepitant compound. The preparation method comprises the following steps: putting aprepitant and copovidone into a mixer, and mixing for 5-8min in an environment with the temperature of 40-60 DEG C; cooling a mixture A to 60-70 DEG C, filtering, putting the mixture A in a stirrer at the temperature of 100-120 DEG C again, adding melatonin into the stirrer, and evenly mixing and stirring; heating the obtained mixture for 5-8min, adding polysaccharide again, and evenly mixing and stirring to obtain a mixture B; then, transferring the mixture B into an extruder again, extruding at the temperature of 20-30 DEG C, enabling the extruded product to stand in an environment with the temperature of 5-8 DEG C for 120-140min, cooling and curing to obtain the aprepitant compound. The method provided by the invention is simple and convenient, suitable for industrial production and high in yield, and can effectively reduce the unnecessary waste.