The invention relates to a preparation method of (S)-(-)-1,1,2-triphenyl-1,2-ethanediol. The preparation method is characterized by comprising the following steps: respectively dissolving methyl mandelate and phenyl
magnesium bromide in solvents to prepare a methyl mandelate solution and a phenyl
magnesium bromide solution; feeding the prepared methyl mandelate solution and the prepared phenyl
magnesium bromide solution into a first micro-channel reactor respectively through a
metering pump so as to perform main reaction, and enabling the reaction solution obtained after the reaction to directly flow into a second micro-channel reactor; feeding an acidic
aqueous solution into the second micro-channel reactor through a
metering pump so as to perform
quenching reaction while the reaction solution flows into the second micro-channel reactor, layering the reaction solution obtained after the
quenching reaction, and taking an organic phase;
drying the organic phase, and then, performing vacuum concentration; and performing recrystallization with
toluene to obtain the finished product (S)-(-)-1,1,2-triphenyl-1,2-ethanediol. The preparation method provided by the invention has the advantages of high yield and fast reaction.