Supported ruthenium catalysts which showed high activity for high-molecular-weight hydrocarbon synthesis from CO and H-2 are studied in under gas-phase, liquid-phase, and supercritical-phase reaction conditions. The calcination temperature effect of the catalysts is investigated. The supercritical phase reaction process is most favorable for high-molecular-weight hydrocarbon synthesis, due to its stable activity, strong extraction capacity and high mass transfer efficiency. Addition of a small amount of middle olefins into a supercritical-phase Fischer-Tropsch (F-T) reaction medium significantly promotes carbon-chain growth and greatly enhances the selectivity of waxy products with slightly-decreased CO conversion, while suppressing methane selectivity and carbon dioxide selectivity. The hydrocarbon products thus formed exhibit anti-ASF distribution.