Magnetic nanocomposites have attracted much attention in the field of wastewater treatment due to their great advantages of fast and efficient removal and separation. Therefore, Fe₃O₄ magnetic nanocomposites coated with fulvic acid (Fe₃O₄/FA) were applied to remove ammonia nitrogen, phosphate and basic blue 3 (BB3) from the effluent. The performance of the adsorbents towards the pollutant removal under different contact time, pH, ionic strength and temperatures were investigated. The whole process with adsorption kinetics and adsorption thermodynamics were also studied. The results showed that the adsorption equilibrium could be achieved in 180 min. The high susceptibility of ammonia nitrogen, phosphorus and BB3 to the alternation of pH, ionic strength and temperatures indicated that electrostatic interaction played a dominant role in the process. Fe₃O₄/FA exhibited excellent adsorption performance for ammonia nitrogen, phosphorus and BB3, and the q_max obtained by the Langmuir model were 106.21 mg/g, 116.81 mg/g and 203.54 mg/g, respectively. Its adsorption performance remained constant in the treatment of ammonia nitrogen, phosphate and BB3 after consecutive 6 cycles. In practical wastewater treatment, Fe₃O₄/FA improved the removal of ammonia nitrogen and phosphate. Therefore, Fe₃O₄/FA magnetic nanocomposites have a promising application for wastewater treatment.