The invention discloses a magnetic carbon modified magnesium iron hydrotalcite composite material and a preparation method and application thereof. The composite material is prepared from magnesium iron hydrotalcite and magnetic carbon loaded on the magnesium iron hydrotalcite, wherein the magnetic carbon is prepared from carbon nano particles and Fe3O4 nano particles loaded on the carbon nano particles. The preparation method comprises the steps of preparing the magnetic carbon and a mixed solution thereof; and preparing the magnetic carbon modified magnesium iron hydrotalcite composite material by using a Fe(NO3)3.9H2O solution, a Mg(NO3)2.6H2O solution and the mixed solution of the magnetic carbon. The composite material has the advantages of environmental protection, good adsorbability, good stability, and easy preparation and the like. The preparation method has the advantages of easily controlled reaction conditions, simple operation, low cost, low energy consumption, short preparation time and the like. The composite material can be used for treating heavy metal wastewater, and has advantages of high removal rate, high removal rate, convenient operation, low cost, no secondary contamination and the like, thereby having good use value and an application prospect.