Abstract: The effects of space velocity in syngas reduction on the reaction performance of the Fischer-Tropsch synthesis (FTS)over a spray-dried spherical Fe/Cu/K/SiO₂ catalyst and on the bulk compositions of the reduced and used catalysts were investigated in a continuous stirred slurry reactor under reaction conditions of 250—280 ℃, 1.5 MPa, H₂/CO=0.67 and 2.0 L•（g cat）^-1•h^-1. The results showed that the BET surface area of the reduced catalysts decreased with the increase of the space velocity in reduction, and the reverse trend for the average pore diameter was observed. The space velocity in syngas reduction did affect the reduction process. The catalyst was easier to be reduced at a higher space velocity. The higher partial pressure of CO₂ in slurry reactor during reduction could partially oxidize the iron carbide. And the content of Fe³⁺⁽spm) was higher in the reduced catalyst. The space velocity in syngas reduction had no obvious effect on the hydrocarbon selectivity, and the effect of the space velocity in syngas reduction on the catalyst activity and stability was significant. The deactivation rate of the catalyst was higher at both lower and higher space velocity. The appropriate space velocity in syngas reduction was 1.0—2.0 L•（g cat）^-1•h^-1.