In this study, phthalic anhydride was reduced by sodium borohydrid,then condensed with ethyl chloroformate on the effect of KHMDS, the product of the condensation was then hydrolysesed to give the phthalide-3-carboxylic acid which was the final target compounds. The effects of reducing agent proportion and reaction time on the yield of the reduction were studied,and also the effects of reagent mole ratio,reaction temperature and reaction time on the yield of the condensation were studied.After 3 steps,the total yield could reach up to 64.2%, the reaction condition was mild, and sodium cyanide which was the violent in toxicity was avoided to use,the structure of the targer compound was confirmed by means of ESI-MS and 1HNMR.