The utilization of sucrose, an easily accessible disaccharide, in the production of a versatile platform chemical lactic acid (LA), is more attractive than a monosaccharide. In this work, we report a modification approach by 3-aminopropyltrimethoxysilane to introduce an amino group onto the surface of the Sn-Beta Lewis acid catalyst. Using the modified catalyst, a maximum LA yield of 58% was achieved under optimal hydrothermal conditions (190 °C, 4 h) from sucrose, along with a complete conversion and a reduced 5-hydroxymethylfurfural (HMF) yield of 8% compared to Sn-Beta. To evaluate the role of the amino group, different substrates were used as the reactants to produce LA. The experimental results suggested that both fructose and glucose were crucial intermediates in the initial 2 h, whereas glucose is the sole reactant after 2 h. Upon modification, not only the hydrolysis of sucrose was promoted, but the side reaction of HMF formation was also suppressed.