Abstract: A method for preparing acetic acid by catalyst including the following steps is provided, S1. preparing the hydrotalcite carrier by hydrothermal method; S2. ion exchange; S3. liquid phase reduction; S4. placing the CoPd/LDH catalyst obtained in S3 in a two-channel fixed bed step-by-step continuous reactor, carrying out the reaction at 100-400° C. and 0.1-20 MPa, synthesizing acetic acid by alternating feeding of CH4+H2+H2O and CO2+H2+H2O, with the alternating time of 50-300 s. The present invention replaces the traditional process of acetic acid production including the steps of methane and carbon dioxide reforming to produce syngas. The process flow is short, the reaction conditions are mild, and the energy consumption and cost are greatly reduced.