The invention discloses a dry-method asphalt mixture modifier and a preparation method thereof as well as an asphalt mixture. The dry-method asphalt mixture modifier comprises the following raw materials in parts by weight: 35-70 parts of resin, 1-35 parts of a curing agent, 0-2.5 parts of an accelerant, 0-6 parts of a flatting agent, 20-40 parts of fillers and 0-2 parts of an auxiliary agent. The asphalt mixture comprises the following materials in parts by weight: 1-5 parts of the dry-method asphalt mixture modifier, 2-8 parts of matrix asphalt and 87-97 parts of mineral aggregates. The prepared dry-method asphalt mixture modifier adopts a dry-method modification technology, is powdery, has a small grain diameter and is easy to disperse in the asphalt mixture; the asphalt mixture prepared from the modifier is simple in operation process, can be continuously produced and is low in cost.