The Fe3O4 magnetic powder was prepared with simple co-precipitation oxidation method using steel pickling waste liquor as raw material. The ratio of Fe3+∶Fe2+ in the reaction solution was monitored by the change of pH during the reaction process，which provided a simple operation for the co-precipitation oxidation method. The catalytic effect of Fe3O4 with small particle size and Alfa reagent grade of 50~100 nm on the synthesis of coumarin derivatives and quinoxaline derivatives was compared. The prepared Fe3O4 samples were characterized by VSM，XRD and TEM. The structures of the compounds were con-firmed by nuclear magnetic resonance spectroscopy (NMR) and high resolution mass spectrometry (HRMS).