Abstract: Biodiesel was prepared continuously in an ultrasonic tubular reactor with calcined Zn-Mg-Al hydrotalcite as catalyst and Jatropha oil as raw material with high acid value. Assisted with ultrasonic radialization, the optimized conditions for biodiesel production catalyzed by calcined Zn-Mg-Al hydrotalcite were obtained. Experimental results showed that at the optimized conditions, i.e., ultrasonic power 210 W, methanol to Jatropha oil molar ratio 4:1, catalyst concentration 1.2% and reaction temperature 60℃, the yield of biodiesel was 94.3%. On the optimized conditions, biodiesel could be continuously produced with Jatropha oil as raw material, the specification of biodiesel after purification completely met German biodiesel standard DIN V 51606: 1997 and the physicochemical properties were stable. The acid value, density, viscosity and chemical compositions of biodiesel stored for 1 year were invariable.