As a sustainable and short-flow process, iron-catalyzed direct conversion of CO-rich syngas to lower olefins without intermediate steps, i.e., Fischer–Tropsch-to-Olefins(FTO), has received increasing attention. However, its fundamental understanding is usually limited by the complex crystal phase composition in addition to the interferences of the promoter effects and inevitable catalyst deactivation. Until recently,the combination of multiple in-situ/ex-situ characterizations and theoretical studies has evidenced H?gg iron carbide(χ-Fe_5C_2) as the dominant active phase of iron-based Fischer–Tropsch catalysts. This perspective attempts to review and discuss some recent progresses on the nature of χ-Fe_5C_2 catalyst and the crucial effects of promoters on the FTO performance from theoretical and experimental viewpoints,aiming to provide new insights into the rational design of iron-based FTO catalysts. As a sustainable and short-flow process, iron-catalyzed direct conversion of CO-rich syngas to lower olefins without intermediate steps, ie, Fischer-Tropsch-to-Olefins usually limited by the complex crystal phase composition in addition to the interferences of the promoter effects and inevitable catalyst deactivation. Until recently, the combination of multiple in-situ / ex-situ characterizations and theoretical studies has evidenced H? gg iron carbide (x- Fe_5C_2) as the dominant active phase of iron-based Fischer-Tropsch catalysts. This perspective attempts to review and discuss some recent progresses on the nature of χ-Fe_5C_2 catalyst and the crucial effects of promoters on the FTO performance from theoretical and experimental views. aiming to provide new insights into the rational design of iron-based FTO catalysts.