The invention provides a preparing method of (S)-3-hydroxy 
tetrahydrofuran, which comprises the following steps: (1) adding (S)-4-Cl-3-hydroxy 
ethyl butyrate, 
potassium carbonate, 
benzyl chloride and DMF into a tri-opening 
bottle, stirring, refluxing, reducing pressure, standing, 
drying after washing, and recrystallizing; (2) adding 
tetrahydrofuran and 
sodium borohydride into a 
tetra-opening 
bottle; stirring and dropwise adding (S)-4-Cl-3-benzyloxy 
ethyl butyrate, continuing to stir, performing rotary 
evaporation condensing, cooling, neutralizing after stirring, extracting, and rectifying after rotary 
evaporation condensing; (3) adding (S)-4-Cl-3-benzyloxy-1-
butanol, water and concentrated 
hydrochloric acid into a tri-opening 
bottle, starting stirring, heating, then performing temperature preserving reaction, neutralizing, extracting, and distilling after rotary 
evaporation condensing; (4) dissolving (S)-3-benzyloxy 
tetrahydrofuran in tetrahydrofuran, adding 
palladium carbon, introducing 
hydrogen, stirring to react, filtering, concentrating under reduced pressure, adding the recrystallized product, filtering after icy bath cooling, and 
drying to obtain the (S)-3-hydroxy tetrahydrofuran. The 
intermediate product is easy to separate and the yield is higher.