Aromatics produced from syngas have been attracting much more attention in recent years. In this study, the K-modified FeMnO/MoNi-ZSM-5 catalyst was used in the one-step conversion of syngas to aromatics. The effects of K loading contents on the catalytic activity and the stability of the FeMnO/MoNi-ZSM-5 catalyst were investigated. In addition, the conversion of CO and the selectivity of the products were analyzed. XRD, EDS, TG, XPS, and BET were carried out to characterize the properties of the catalysts before and after reaction. It can be investigated that the loading of K promoted the CO adsorption performance and the carburization of iron oxide on the catalyst, which increased the stability of the catalyst and inhibited the formation of CH4 and CO2.