The dependencies of hydrocarbon product distributions of alkali promoted iron catalyst in Fischer-Tropsch synthesis have been studied. The concept of two superimposed Anderson-Schulz-Flory distributions has been applied for the representation of the effects of Mg, La and Ca promoters on product distributions. The FTS performance of the catalysts was tested in a fixed bed reactor under the conditions 563 K, 1.7 MPa, H2/CO = 1 and space velocities 4.86 and 13.28 nl h-1 gFe-1 . The results indicate that appropriate amounts of these promoters enhance the break in ASF distributions in the order Ca > Mg > La because of the rising of the catalyst surface basicity. The dependencies of hydrocarbon product distributions of alkali promoted iron catalyst in Fischer-Tropsch synthesis have been studied. The concept of two superimposed Anderson-Schulz-Flory distributions has been applied for the representation of the effects of Mg, La and Ca promoters on product distributions . The FTS performance of the catalysts was tested in a fixed bed reactor under the conditions 563 K, 1.7 MPa, H2 / CO = 1 and space velocities 4.86 and 13.28 nl h-1 gFe-1. The results indicate that appropriate amounts of these promoters enhance the break in ASF distributions in the order Ca> Mg> La because of the rising of the catalyst surface basicity.