TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The phytosterol is stigmasterol, beta -sitosterol, campesterol and brassicasterol. The fatty acid comprises saturated fatty acid e.g. caproic acid, octylic acid, decanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachic acid and behenic acid and unsaturated fatty acid e.g. oleic acid, linoleic acid, linolenic acid, eicosenoic acid and erucic acid. The ionic liquid is 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium trifluoromethylsulfonate or choline chloride-metal chloride ionic liquid of formula (ChCl.xMCln) (I), preferably choline chloride-stannous chloride ionic liquids of formulae (ChCl.2SnCl2) (II) and (ChCl.2.5SnCl2) (III), choline chloride-zinc chloride ionic liquid of formula (ChCl.2ZnCl2) (IV) and choline chloride-ferric chloride ionic liquid of formula (ChCl.2FeCl3) (V), and the amount is 5-10% of the mass of the phytosterol ester.ChCl = choline chloride;x = 2 or 2.5;M = Sn, Zn or Fe; andn = 2 or 3.Preferred Method: (I) is prepared by uniformly mixing 20 mmol of choline chloride and 40 mmol of stannous chloride, zinc chloride or ferric chloride under magnetic stirring, heating to 100 degrees C to obtain colorless ionic liquids (II), (IV) and brown colored ionic liquid (V), uniformly mixing 20 mmol of choline chloride and 50 mmol of stannous chloride, heating to 100 degrees C, stirring to obtain colorless and clear ionic liquid (III). The molar ratio of acid alcohol is 1:1-4:1, the reaction temperature is 90-170 degrees C, and the reaction time is 2-8 hours. The separation and purification process comprises dissolving the phytosterol ester mixture in a developing solvent (material-liquid ratio is 1:3 wt./vol.), where the developing solvent is the mixture of petroleum ether/ethyl acetate (9:1 vol./vol.), and column is silica gel column, collecting the product, performing thin layer chromatography to the collected product, combining the similar components, rotary steaming to remove the solvent to obtain the phytosterol ester pure product, and identifying the pure product by the infrared, mass and nuclear magnetic resonance spectroscopic analysis. The method comprises processing the quantitative thin layer chromatography and quantitative HPLC to the product to detect the reaction process, where the HPLC quantitative analysis utilizes external standard method, and self controlling standard product. The analysis of the sample comprises the conversion rate analysis of the phytosterol in the esterification, yield analysis of the phytosterol and content analysis of the side-product (mainly the diolefin product produced by dehydration during esterification) in the reaction process. The preparation of unsaturated fatty acid phytosterol ester comprises detecting the esterification yield, detecting the anisidine value in the reaction system by IS06885 method to detect the oxidized degree of the unsaturated fatty acid in the system.