•Co–CaO/AC catalysts were prepared and used for the production of mixed higher alcohols.•The CaO facilitated the generation of the hcp Co species during the activated process.•The CaO species promoted the development of the Co2C species during the reaction.•The 15Co0.1Ca/AC catalyst shows the excellent performance for the alcohols synthesis.•The synergistic effect of Co0 and Co2C are responsible for the alcohols synthesis.An alternative CaO-promoted Co/AC catalysts with high selectivity of C1–C16 alcohols were synthesized and systematically studied. The catalysts were characterized by means of N2-physisorption, XRD, H2-TPR, CO-chemisorption and HRTEM. Then the activated catalysts were used in the CO hydrogenation reaction for the alcohols synthesis. Reaction results showed that CaO promoter improved the yield of C1–C16 alcohols significantly from 9.9% to 15.0% in comparison with un-promoted Co/AC catalyst. Characterization results indicated that the addition of CaO promoted the formation of hcp metallic Co, which was further liable to conversion into Co2C species. It was suggested that Co2C species was related to synthesis of alcohols. It was found that the appropriate relative ratio of Co2C/Co was beneficial to synthesis of mixed C1–C16 alcohols over the CaO-promoted Co/AC catalysts. The synergistic effect of metallic Co nanoparticles and Co2C species, which contact intimately, is responsible for the alcohols synthesis.