NOVELTY - An alpha -terpinol is prepared by dissolving alpha -terpinol in solvent and then in detaching agent in solvent, stirring, heating, and filtering to obtain filtering solution and filtering slag; distilling filtering solution to obtain solid; adding same solvent in solid to form saturated solution, crystallizing, and filtering to obtain crystal; recrystallizing the crystal; dissolving recrystallized crystal in eluting agent and stirring, heating to separate phases to obtain organic phase and water phase, distilling organic phase, and recycling eluting agent to obtain levogyrate alpha -terpinol.    USE - Method for preparing alpha -terpinol (claimed) useful as green synergist of agricultural miscible oil or water type pesticide with respect to vegetable and fruit, or used as medical synergist of analgesic and antiinflammatory.    ADVANTAGE - The method is capable of preparing alpha -terpinol having high optical purity. The reaction step and eluting step are performed at room temperature and the used solvent, eluting agent and detaching agent can be used repeatedly. The method has simple and safe operation, easy follow-up processing process, low solvent and eluting agent loss, and low cost.    DETAILED DESCRIPTION - Preparing alpha -terpinol having high optical purity, comprises:    (A) dissolving alpha -terpinol in solvent and then in detaching agent in the solvent, stirring for 36-60 hours at room temperature, heating for 6-12 hours, and filtering to obtain filtering solution (A) and filtering slag (B);    (B) distilling filtering solution (A) in reduced pressure to obtain solid (C);    (C) adding same solvent in solid (C) to form saturated solution, crystallizing at 4-10 degrees C, and filtering to obtain crystal (D);    (D) repeating step (C) and recrystallizing the crystal (D);    (E) dissolving the recrystallized crystal in eluting agent and stirring for 1-2 hours at room temperature, heating to separate the phases to obtain organic phase and water phase, distilling the organic phase in reduced pressure, and recycling the eluting agent to obtain levogyrate alpha -terpinol having high optical purity;    (F) washing the filtering slag (B) with same solvent to obtain solid (E) and recrystallizing solid (E) to obtain crystal (F);    (G) dissolving crystal (F) in eluting solution and stirring for 1-2 hours at room temperature, heating to separate the phase to obtain the water phase and the organic phase, distilling the organic phase in reduced pressure to obtain dextral alpha -terpinol having high optical purity; and    (H) cooling, crystallizing and filtering the water phases in steps (E) and (F) which is condensed in reduced pressure to obtain solid detaching agent.    The solvent is 1-4C low-carbon alcohol. The detaching agent is N,N,N-trimethyl-1-hydroxy-3-methyl-2-butyrobetaine, and a molar ratio of the detaching agent and alpha -terpinol is 1-1.5:1. The eluting agent is mixed solvent of ether, dimethyl ether, isopropyl ether, butyl ether and water.