The invention discloses a reactive dye wastewater adsorbing agent and a preparation method thereof. The reactive dye wastewater adsorbing agent is an iron complex containing an ionic liquid group and a hydroxyl group, synthesized through ionic liquid solidification and hydroxylation. The reactive dye wastewater adsorbing agent can be used as an adsorbing agent for treating reactive dye wastewater, is simple in preparation process, mild in synthesis conditions, and easy to realize, has a relatively strong adsorption function for reactive dye, and can be used for decoloring the reactive dye wastewater. Meanwhile, the hydroxylated imidazolyl ionic liquid iron complex adsorbed with the dye can be recycled only by simple treatment.