In this study, bamboo powder (BP), bamboo parenchyma cells (PCs), and bamboo fibers (BFs) were used as precursors to prepare activated carbon by ZnCl2 one-step activation to investigate the differences in the pore structures of the three. The results showed that BFs-based activated carbon had a higher specific surface area (2129 m2/g). Subsequently, the activation reaction paths of the BFs-based activated carbon preparation process were analyzed and explored by TGA, XRD, TG-MS-FTIR, EA, and other analytical methods, and the reaction mechanism was inferred. The results showed that the main reaction below 220 °C was the breaking of molecular bonds of oxygen-containing functional groups on hemicellulose, and the pyrolysis by-products at this stage were dominated by small molecules such as H2O, CO2, CH4, CH3OH, and HCHO. The pyrolysis of cellulose and the activation reaction of ZnCl2 were the main reactions between 220 °C and 650 °C. ZnCl2 was a strong dehydrating agent that can form ZnOCl2·2 H2O with intramolecular water molecules, and gradually decompose to form ZnO with the increase in temperature, the main gaseous products in this temperature interval were mainly H2O, CO, CO2, C3H4, and CH4. Above 650 °C, pyrolysis was basically completed and continued to shift to the aromatic structure, with the gaseous products mainly being H2, H2O, CO2, CH4, CO, C3H4, and a small amount of CH3OH and HCHO. Display omitted •The reaction mechanism in the activation of bamboo fibers by ZnCl2 was studied.•The staged pyrolysis process of BFACs was analyzed and summarized.•220°C-650 °C as the main stage of activation.•The gases produced in each pyrolysis stage were analyzed using TG-MS-FTIR.•Possible reactions in the activation of bamboo fibers by ZnCl2 were proposed.