The invention provides a preparation method for a binary sucrase inhibitor. The preparation method comprises the following steps: subjecting fresh mulberry leaves to triturating, pulp refining, enzymatic hydrolysis, separating, ion-exchange fiber extraction and concentration so as to obtain a mulberry leaf concentrate containing 25 to 30% of 1-deoxynojirimycin; then mixing the mulberry leaf concentrate with L-arabinose crystal according to a ratio of 1: 4500-5000 and carrying out melting and uniform mixing under stirring; drying the obtained mixture in a vacuum drier for 2 to 4 h; and carrying out crushing and screening so as to obtain the binary sucrase inhibitor with a size of 100 to 150 meshes. The binary sucrase inhibitor has quick-water-solubility and a high sucrase inhibition rate, can perfectly inhibit hydrolysis of cane sugar in the stomach and shows wide application prospects.