B crystal form epalrestat and preparation method thereof

The invention provides B crystal form epalrestat and a preparation method thereof. The method comprises the following steps: taking rhodanine acetic acid and alpha-methylcinnamaldehyde as raw materials and reacting to generate epalrestat crude product suspension; adding a first acid solution into the epalrestat crude product suspension; then heating and melting, carrying out centrifugal treatment,washing a filter cake and drying to obtain an epalrestat crude fine product, wherein the mole ratio of an acidic substance in the first acid solution to the rhodanine acetic acid is (3 to 4.5) to 1;adding low-carbon alcohol into the epalrestat crude fine product; after heating and melting, keeping for pre-set time; then cooling to 20 to 30 DEG C; carrying out the centrifugal treatment and dryinga filter cake to obtain an epalrestat fine product. According to the B crystal form epalrestat and the preparation method thereof, provided by the invention, the yield and purity of B crystal form epalrestat products are easy