<p>Effect of acid impregnation and mechanical milling on the hydrolysis behavior and products distribution of chitin in subcritical water was investigated by a “temperature-programmed hydrolysis process”, in the present study. The acid impregnation and mechanical milling efficiently destroyed the glycosidic and hydrogen bonds in chitin, leading to a loss of crystal structure and significantly increased water solubility. The loss of crystal structure rendered the pretreated chitin substrates more susceptible to hydrolysis in subcritical water compared to raw chitin, thereby reducing the activation energy required to initiate the hydrolysis reaction. The main compounds in hydrolysate were analyzed to be reducing sugar, antioxidant compounds, 5-hydroxymethylfurfural, isopropyl acetate, acetamide and propanoic acid ethyl ester. The possible mechanism of acid impregnation and ball milling for hydrolysis of chitin in subcritical water was also proposed. This work suggested that acid-mechanical milling is an efficient pretreatment process for accelerating the liquefaction of chitin to valuable chemicals in subcritical water.</p> Graphical abstract <p></p>