The Fischer-Tropsch syntheses over silica-supported iron catalysts were carried out in an atmospheric reactor at 270℃. The catalytic activity extended to steady-state value after 10-20 hour reaction. The longer reduction period and the higher reduction temperature made the catalytic activity more stable, and even unreduced catalyst showed similiar activity. K-promoted catalysts showed higher olefin selectivity and increased CO₂ production rate with little decrease of activity. The maximum olefin selectivity of 53.5% was obtained at space velocity of 9600h^-1, H₂/CO=2.