The invention discloses an extracting method for soybean oligosaccharides. The method comprises the following steps of preprocessing, ultrasonic-microwave synergic processing, acid precipitate processing, digestion processing, decoloring, salt removal, concentration drying, MPLC separation and secondary MPLC separation. According to the extracting method for soybean oligosaccharides, dissolution of oligosaccharide is accelerated by means of the ultrasonic effect, meanwhile, the temperature is controlled within the proper range, the soybean cell wall is softened, the soybean structure is loosened, molecular movement is violent, the soybean oligosaccharides are more likely to be leached, the soybean oligosaccharides extracting rate is increased, by adopting ultrasonic-microwave synergic processing, ultrasonic vibration mass transfer and microwave energy transfer are combined, soybean oligosaccharides extraction is facilitated, oligosaccharides are separated through the MPLC, crude soybean oligosaccharides can be effectively separated into stachyose monomers, raffinose monomers and saccharose monomers, and the monomers of oligosaccharides can be applied separately.