This paper aims to establish a efficient and green method to remove sulfamethoxazole (SMZ) in water environment. The Fe3O4 magnetic nanoparticles were synthesized via a solvothermal method, and the structure and morphology of the prepared materials were characterized by a series of techniques including XRD, magnetic performance testing, SEM and TEM. The catalytic oxidation characteristics of SMZ in the heterogeneous Fenton system of Fe3O4-H2O2, as well as the influences of the variables such as pH value, H2O2 concentration and catalyst dosage on the degradation processes were investigated. The results showed that the prepared Fe3O4 nanoparticles were microspherical with an average particle size of about 250 nm, it has strong paramagnetism and could effectively activate H2O2 to produce ·OH, which could degrade SMZ efficiently. In the Fe3O4-H2O2 oxidation system, 20 mg/L of SMZ was almost completely degraded within 5 min under the condition of pH at 3, and a Fe3O4 dosage of 1.0 g/L and a H2O2 dosage of 5.0 μL/mL at 25 ℃. The cycle experiments showed that the synthesized samples possessed the excellent stability. The experimental results in this study could provide some theoretical references for SMX removal in the aqueous environment.