In order to extract more isoflavones from soybean cake, the ultrasonic technology were used. The soybean isoflavones were extracted from fermented soybean cake by ultrasonic technology, and the influences of extraction solvent and extraction time,ratio of sample to extractant and the number of repeated extraction were studied by single factor and systematial lineartest.The results showed that the optimum extraction technology was as follows: solvent: 80% ethanol;extraction time:20 min;the ratio of sample to solvent: 1:15(g:ml);repetition of extraction: 2 times. The extraction rate of this method can reach 0.548%.