The invention relates to a method for preparing high-purity acrylonitrile, which mainly solves the problems that acrylonitrile raw material treatment capacity is low in the process of removing aldehyde, hydrocyanic acid, acetone, acrolein, methacrylonitrile, oxazole, propionitrile, butene nitrile, a polymerization inhibitor, peroxide, iron ions and other trace impurities from the acrylonitrile raw material, or new compounds are introduced and new impurities of the acrylonitrile raw material are increased but a method for simultaneously removing various trace impurities from the acrylonitrile raw material is absent, and the like in the prior art. The method comprises the following steps of: a) contacting the acrylonitrile raw material with cation exchange resin to obtain a material flow I from which the oxazole is removed; b) contacting the material flow I with anion exchange resin to obtain a material flow II from which the acrolein is removed; c) contacting the material flow II with alumina to obtain a material flow III from which the peroxide and water are removed; and d) rectifying the material flow III by using a rectifying tower, and performing side stream gas phase production at a position of 5-15 plates of the rectifying tower (counted from bottom to top) to obtain the high-purity acrylonitrile which has the purity of 99.99 percent and from which the aldehyde, the hydrocyanic acid, the acetone, the acrolein, the methacrylonitrile, the oxazole, the propionitrile, the butene nitrile, the polymerization inhibitor, the peroxide and the iron ions are removed. The technical scheme solves the problems; and the method can be applied to industrial production of purification treatment of high performance polyacrylonitrile-based carbon fiber materials.