Bimodal pore Fe-Mn-K catalysts supported onto SiO2 pellet were prepared by a one-step incipient wetness impregnation method. In this method, the active component and promoters were used as the "bricks" to directly build up the small pores inside the large pores of silica gel. The catalysts were applied to catalyze Fischer-Tropsch synthesis in slurry phase. Compared with the SiO2 supported non-bimodal catalysts, the bimodal catalysts exhibited excellent activity due to the improved active metal dispersion and the fastened diffusion efficiency. The preparation method was much more feasible than the previous two-step method, and can be extended to prepare bimodal catalysts with different active components.