A novel photocatalyst SnO2/SrFe12O19 (SS) was fabricated by a two-step hydrothermal method, and was characterized by XRD, SEM, EDS, XPS, BET, UV-Vis DRS. The photocatalytic activity was assessed through degrading solution of Rhodamine B (RhB) under simulated solar irradiation. The results showed that composite of wt 5% SrFe12O19 (SS-5) had superior photocatalytic activity, and the degrading ratio could reach 83.8% within 120 min, which was more than the pure phase SnO2. Moreover, specific surface area, cumulative pore volume, and average adsorption pore size of SS-5 slightly enhanced, the light absorption range expanded to the visible light direction, and the band gap energy decreased. Meanwhile, the VSM test showed that the magnetization saturation of SS-5 was 1.42 emu/g, and magnetic separation could be achieved. In the photocatalytic degradation process, RhB was successfully degraded under the effect of superoxide radical (·O2−), and photogenerated hole (h+). Based on these findings, possible photocatalytic mechanism was investigated and explained. The fabricated SnO2/SrFe12O19 could be used as a valuable photocatalyst for the treatment of sewage.