A series of potassium-promoted, MgO-supported Fe-Mn catalyst were prepared by the wetness impregnation method and characterized by nitrogen adsorption, TPR and X-ray photoelectron spectroscopy (XPS) techniques. The CO hydrogenation activity test indicated that with the addition of potassium, significant changes in CO conversion and selectivity to light alkenes are observed. 2 wt.% potassium-promoted Fe-Mn catalyst exhibited better catalytic performance. The CO hydrogenation reaction temperature and space velocity were also investigated and optimized.