The invention discloses a method for preparing spherical aluminum nitride powder under the assistance of high atmospheric pressure and a fluoride additive, belonging to the technical field of preparation of non-oxide ceramic powder materials. The method concretely comprises the following steps: evenly mixing aluminum oxide, a carbon source and fluoride additive through a ball-milling technology, drying and then putting in a graphite crucible, transferring into an atmospheric-pressure sintering furnace, performing carbon thermal reduction reaction for 1-6 hours in the nitrogen atmosphere, and maintaining the pressure of nitrogen to be 0.2-2MPa, and the reaction temperature to be 1650-1900DEG C; and after the reaction is completed, putting the obtained product into a muffle furnace, carrying carbon emission for 1-5 hours under the condition of 500-750DEG C, thus obtaining the spherical aluminum nitride powder. The prepared aluminum nitride powder has the characteristics of being high in spherical degree, smooth in the surface, even for particle size distribution and the like, the intermediate particle size is 3-10mu m, and the spherical degree achieves more than 80%; the spherical aluminum nitride powder is very suitable as high-heat-conducting aluminum nitride filler; in addition, the technological method is simple, the raw material cost is relatively low, and large-scale industrial production can be realized.