The effect of reaction pressures on structure-performance of Co2C-based catalyst for syngas conversion was studied in detail. Co2C nanoprisms with exposed facets of (101) and (020) used for the dissociation adsorption of CO molecules were stable at low reaction pressure, and promising FTO (Fischer-Tropsch to olefins) performance with low CH, selectivity and high C-2-4(=) selectivity simultaneously was achieved. With the increase of reaction pressure, the oxygenates selectivity significantly increased at the expense of decreasing C-2-4(=) selectivity. The characterization results indicated that the morphology of Co2C nanostructures changed from nanoprisms to nanospheres and that the metallic Co-0 was observed with the increase of reaction pressures. The appearance of Co2C(111) benefited CO insertion, and the formation of Co/Co2C(111) as dual active sites contributed to the enhancement of oxygenates selectivity at elevated pressure. This study suggested that reaction pressures had a strong effect on structure-performance of Co2C-based catalyst for syngas conversion.