A potassium- and copper-modified iron-based catalyst (K-Cu-Fe/SiO2) was synthesized by the co-precipitated method. The general structural properties of the catalyst were characterized with various techniques, including SEM, XRD, H-2-TPR, N-2 adsorption-desorption and Raman spectroscopy. The results reveal that the fresh catalyst is mainly composed of alpha-Fe2O3 phase with rod-shaped morphology formed by nanoparticles. The effect of activation process on the Fischer-Tropsch synthesis catalytic performance was then investigated. It shows that activation process has an important influence on the reactive stability. The in situ XRD and in situ Raman spectroscopy were used to study the structural changes of the Fe-based catalyst during reduction and reaction processes. The Fe2C iron carbide as the main active phase was observed after reduction process. [GRAPHICS] .