The invention relates to a method for preparing AlN nanopowder by adopting high-energy ball milling under assistance of plasma and belongs to the technical field of nanometer preparation. According to the method, a bipolar nanosecond-level high-voltage marrow-pulse power supply or an alternating current power supply is taken as driving source under barometric pressure, dielectric barrier discharge plasma is obtained in nitrogen or mixed gas of the nitrogen and argon so as to assist the high-energy ball milling to prepare the AlN nanopowder. The method has the advantages that the operation is simple, the cost is low, the grain size of the AlN nanopowder is smaller than that of aluminum nitride prepared by only adopting ball milling, the malposition defect is large, the internal energy of the grain is high, the required temperature of carbon thermal reduction reaction is low, the conversion rate is high, and the like.