A series of Co/CNT catalysts with different calcination temperature were prepared by the impregnation method to investigate the impact of different calcination temperature on the thermal stability, structure, phase, reduction degree and Fischer-Tropsch synthesis reaction activity. The catalyst characterization techniques include differential thermogravimetric analysis (TGA), nitrogen physisorption, X-ray diffraction (XRD), temperature program reduction (TPR), scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). These characterization results show that carbon nanotube was stable below 500℃. When calcined at 250~500℃, surface area of the catalysts is in the range of 79.78~85.23 m2/g, pore volume in the range of 0.6~0.7 m3/g, and pore diameter in the range of 28.9~33.4 nm. The largest pore size is found when calcined at 350℃. When calcined at 350℃ the main phase of the catalyst is Co3O4 and CoO. The resulted crystallite size is relatively small, and crystallite size distribution is relatively narrow. TPR results and Fischer-Tropsch synthesis reaction data show that calcination at 350℃ lead to the lowest reduction temperature and highest CO conversion (12.5%).