NOVELTY - Pregnenolone acetate (I) is synthesized by reacting pregnenolone derivative (II) in acetic anhydride and acetic acid at 180-220 degrees C and 0.6 MPa for 0.5-2 hours; decompressing, distilling and recycling acetic anhydride and acetic acid; adding aprotic solvent for dissolution, then adding photosensitizer and filling oxygen, and irradiating with a filament lamp to obtain pregnenolone reaction product (IV); directly adding acid to (IV) without purifying, or distilling and recycling the aprotic solvent, adding acetic acid for dissolution, and reacting for 8-16 hours at a refluxing temperature.    USE - Method for synthesizing pregnenolone acetate (claimed).    ADVANTAGE - The method can eliminate three-step reaction by a utilizing one boiler process, reduces environmental pollution problem caused by using metal compound and highly poisonous pyridine hydrochloride during reaction process, and avoids harm to operators caused by using highly poisonous solvent acetonitrile and benzene. Further, the method utilizes simple device with convenient operation, involves mild reaction condition, has high total output rate, and is environment-friendly and suitable for industrial production of pregnenolone acetate.    DETAILED DESCRIPTION - Synthesis of pregnenolone acetate of formula (I) comprises:    (A) reacting pregnenolone derivative of formula (II) in acetic anhydride and acetic acid at 180-220 degrees C and 0.6 MPa for 0.5-2 hours;    (B) decompressing, distilling and recycling the acetic anhydride and the acetic acid;    (C) adding aprotic solvent for dissolution, then adding photosensitizer and filling oxygen, and irradiating with a filament lamp to react for 2-4 hours to obtain pregnenolone reaction product of formula (IV);    (D) directly adding acid to compound (IV) without purifying, or distilling and recycling the aprotic solvent, adding acetic acid for dissolution, and reacting for 8-16 hours at a refluxing temperature; and    (E) recrystallizing with methanol or ethanol to obtain compound (I), where molar ratio of compound (II) to photosensitizer is 1:0.005-0.01; molar ratio of compound (IV) to acid is 1:0.05-0.1; the acid is concentrated hydrochloric acid, concentrated sulfuric acid or p-toluenesulfonic acid.    R=H, OH, OAc or carbonyl.    Provided that when R is OH, OAc or carbonyl, 5-6C is C-C single bond and Ac is acetyl.