Organonitrogen chemicals are crucial in pharmaceutical production and material synthesis. However, the current overreliance on the energy-intensive and highly polluting Haber-Bosch synthesis process necessitates an urgent need to explore more sustainable and environmentally friendly methods for producing these chemicals. Herein, we report an effective method for the selective conversion of chitin into its oligomers in deionized water. A systematic investigation was conducted on the pretreatment of chitin using various physical methods, such as microwave, ultrasonic, and ball milling while keeping the power consumption constant. A series of techniques were used to investigate the molecular structure, surface morphology, and depolymerization degree of the pretreated chitin. Results demonstrate that ball milling is the most effective pretreatment method which achieves a significant reduction in the crystallinity and viscosity average molar mass of chitin. These changes are advantageous for the subsequent chitin selective depolymerization reactions. Ball milling chitin with solid acid Fe