The invention discloses a method for preparing alpha-terpineol by catalyzing-free hydration with turpentine oil in subcritical water medium. The procedures of the method are as follows: 1) a high pressure reaction kettle is added with the mixed solvent consisting of the deionized water and the auxiliary solvent, the volume ratio of the deionized water and the auxiliary solvent in the mixed solventis 1:2 to 8: 1, then the turpentine oil is added, the volume ratio of the mixed solvent and the turpentine oil is 2:1 to 7: 1, then the mixture is stirred, a vent valve is opened for two to five minutes when the temperature rises to boil under normal pressure; 2) the vent valve is closed, the temperature continues to rise between 190 DEG C and 250 DEG C, the reaction is made for 3 to 10 hours; 3)the reaction product is cooled and then is made pressure decreasing and fraction to produce the alpha-terpineol. The invention does not need to add any catalyst during the hydration, solves the pollution problem caused by the acid-alkali catalyzation hydration reaction to the environment, has simple reaction process, higher product yield and better purity, and realizes the innocent treatment of production process.