The invention relates to an iron catalyst which contains an assistant and used for catalyzing the Fischer-Tropsch reaction, which is characterized by comprising the components with mass ratios of Fe: Cu; K: Ti: SiO2 equal to 100: (0.1-10): (0.1-10): (0.01-5): (5-30), wherein, Fe, Cu, K and Ti exist in the form of oxides. The invention also relates to a preparation method for the catalyst, which comprises the steps that: at the presence of a precipitator with a pH value of 6-9, ferric nitrate, copper nitrate and a titanium compound are deposited in water; a deposit is separated and mixed with potassium carbonate and silica sol after being washed; a mixture obtained is dried and calcined. The iron catalyst with the assistant of titanium structure has relatively large specific surface area, CO conversion activation and antiwelding and antisulphour properties.