The present invention relates to a method for preparing liquid or solid hydrocarbons from syngas via the Fischer-Tropsch synthesis in the presence of iron-based catalysts, the iron-based catalysts for the use thereof, and a method for preparing the iron-based catalysts; more specifically, in the Fischer-Tropsch reaction, liquid or solid hydrocarbons may be prepared specifically with superior productivity and selectivity for C5+ hydrocarbons using the iron-based catalysts comprising iron hydroxide, iron oxide, and iron carbide wherein the number of iron atoms contained in the iron hydroxide is 30% or higher, and the number of iron atoms contained in the iron carbide is 50% or lower, relative to 100% of the number of iron atoms contained in the iron-based catalysts.