The invention relates to the technical field of steel piece surface treatment, and in particular relates to a preparation method of a high-temperature wear-resistant coating on the surface of a steel piece. According to the preparation method, a composite coating of a Fe-Al intermetallic compound and a little Al2O3 is obtained through liquid dip aluminum plating and subsequent compound dispersion treatment. The process flow of the preparation method comprises pretreatment (alkali cleaning, acid pickling and assisted plating), dip aluminum plating and dispersion treatment, wherein the dip aluminum plating is carried out for 1-10 minutes in liquid aluminum at a temperature ranging from 720 DEG C to 800 DEG C; and compound dispersion annealing which is carried out in a protective atmosphere or in vacuum at a temperature ranging from 850 DEG C to 1100 DEG C for 1-5 hours, and in air at a temperature ranging from 400 DEG C to 600 DEG C for 20-30 minutes. The temperature and the time of the dispersion treatment are adjusted so that composite wear-resistant coatings containing the intermetallic compound and a little Al2O3 and are different in thickness can be obtained. The preparation method has the characteristics of simple and convenient process, low cost, high coating binding force, excellent high-temperature wear resistance and the like, and thus can be widely applied to surface strengthening of high-temperature wear resisting steel pieces.