Abstract: The effect of solvents on the reaction performance of FischerTropsch synthesis under supercritcal and nearcritical conditions was studied in a fixed bed reactor. Two kinds of solvents: pure solvents (n-hexane and n-pentane) and mixed solvents (the solvent consists mostly of n-hexane and some content of C5 to C10 normal paraffins and normal olefins) were chosen as the solvent. The catalyst used was a SiO2 supported cobalt catalyst. The results showed that the partial pressure of n-hexane had little influence on the CO conversion when total pressure and syngas partial pressure were kept constant. 1olefins content in the products, however, increased with increasing partial pressures of n-hexane. 1olefins content in the products under supercritical condition was obviously higher than that under nonsupercritical conditions. Similar CO conversion, CH4 and CO2 selectivities and hydrocarbon distribution were obtained in different pure media: n-pentane and n-hexane. 1olefins content in n-pentane was slightly lower than that in n-hexane. Compared with pure n-hexane solvent, the solvent with mainly n-hexane and some C5~10 components had similar effects on CO conversion, CH4 and CO2 selectivities, and hydrocarbon selectivity of the products. This result suggested that the recycle of the supercritcal solvent contained some content of lighter fractions (such as C5~10) produced in the FT process is possible for reducing the amount of supercritical solvent during supercritical FT process. The binary mixed solvent (25% n-hexane/75% n-decane) showed much higher 1olefins selectivity than the pure n-hexane probably because of its higher solubility to heavier products.