TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The crude crystal of benidipine hydrochloride is prepared by the method, but it is also synthesized through other possible synthetic routes, comprising acyl chloridizing main ring of dihydropyridine and then joining 3-piperidinol and benzyl, one-pot method involving 3-nitrobenzaldehyde, beta -aminocrotonate and acetylacetate, or by synthesis of main ring via beta -aminocrotonate or acetylacetate. The crude crystal of benidipine hydrochloride is re-dissolved in suitable solvent, and then crystallization is performed for at least one time under ultrasound to obtain highly purified benidipine hydrochloride. The crystallization under ultrasound is performed at -78-100 degrees C, preferably at -5-30 degrees C. Preferred Components: The ultrasound technology is introduced into the pre-treatment stage of benidipine hydrochloride synthesis to improve dispersion, dissolution and homogenization of reactants, and to enhance the reaction speed. The solvent is lower-carbon-number ketone, lower-carbon-number alcohol, lower-carbon-number ether, lower-carbon-number acid, lower-carbon-number ester, dichloromethane, chloroform, acetic anhydride or other commonly used small molecule solvents alone or preferably acetone, ethanol, methanol, N,N-dimethylformamide, acetonitrile, diethyl ether, dichloromethane and/or water. The frequency of the ultrasound ranges is 10-500 kHz, preferably 15-100 kHz. The power for the ultrasound is 1 mW to 5000 W, preferably 1-3000 W. The duration of the ultrasound is 1 minute to 24 hours, preferably 3-120 minutes. EXAMPLE - Dihydropyridine main ring ((2,6-dimethyl-4-(3-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylic acid monomethyl ester) (10 g) was placed in reaction flask (200 ml) under ultrasound. N,N-dimethylformamide (14 ml) and dichloromethane (56 ml) were added to the above reaction mixture. To the resultant mixture thionyl chloride (2.4 ml) was added under ice-bath, then stirred for 1 hour to obtain a clear solution. Then, pyridine (alcohol) side chain, ((1-benzyl-3-hydroxypiperidine) (6.3 g) was added and stirred for 2.5 hours under ice-bath. The reaction solution was washed with water (40 ml) and saturated saline solution (40 ml). The dichloromethane solution was dried for 2 hours by adding anhydrous sodium sulfate (4 g). Then, sodium sulfate solid was removed by filtering, and dichloromethane was recycled to obtain crude crystal of benidipine hydrochloride. The crude crystal was dissolved in acetone (100 ml), and was ultrasounded at 150 W and 40 MHz for 7 minutes, filtered under reduced pressure and dried to give crystal purified benidipine hydrochloride (yield 36.2%).