Abstract: A commercial coconut activated carbon was firstly pretreated by HCl with different concentrations. Then the Pd/C catalyst used for purification of terephthalic acid was prepared using immersion method based on the pretreated carbon. By means of SEM, EDS, TEM, XRD and BET techniques, the impact of HCl pretreatment on microstructure and activity of the catalysts was investigated, and the relationship between HCl concentration and catalyst activity was explored. Test results show that the catalytic activity first increases and then decreases with the increase of HCl concentration and the maximum activity was obtained at the HCl concentration of 0.6mol/L. SEM and adsorption-desorption tests show that the pretreatment of HCl can increase the average pore diameter and the mesopore volume of activated carbon. The EDS result indicates that the content of Pd maintains nearly constant, while some O element and trace impurity of Si and Cl appear on the carbon surface after HCl pretreatment. The changes of the surface morphology of HCl pretreated active carbon are not found. Owing to the increase of pore diameter and mesopore volume, the effective surface area of carbon for loading Pd component is increased, which is beneficial to the dispersity of Pd, and to the catalytic activity of Pd/C catalyst.