The invention discloses an in-situ MgO template preparing method and application magnetic mesoporous carbon nanospheres with a high adsorptive property, and belongs to the field of preparing methods of magnetic mesoporous carbon nanospheres. The in-situ MgO template preparing method of the magnetic mesoporous carbon nanospheres with the high adsorptive property comprises the steps that Fe3O4@nSiO2 and a magnesium citrate solid are mixed and ground evenly, the ground mixture is calcined in a nitrogen atmosphere and then washed with HNO3 and high-purity water in sequence, and the magnetic mesoporous carbon nanospheres with the high adsorptive property are obtained, wherein the mass ratio of Fe3O4@nSiO2 to the magnesium citrate solid is (0-5):(5-10). The in-situ MgO template preparing method and application of the magnetic mesoporous carbon nanospheres with the high adsorptive property have the advantages that the method is simple, efficient, low in cost, environmentally friendly, capable of being applied to mass preparation and the like; a prepared magnetic mesoporous carbon nanosphere adsorbing agent has a large specific surface area and a large pore volume and has the advantages of high adsorption capacity, a wide pH range, high adsorption efficiency and the like on the aspects of adsorbing metal ions such as Cu ions and Pb ions; the magnetic mesoporous carbon nanospheres prepared through the method can be applied to the fields such as wastewater treatment, medicine release and catalytic carriers.