In this paper, the Fe₃O₄@C nanoparticles were synthesized by hydrothermal method and then arranged into Fe₃O₄@C photonic crystal films by vertical deposition method, natural deposition method, and magnetic field assisted method, respectively. The vertical deposition method for preparing photonic crystal films is time-consuming, and the resulting films are non-uniform. Additionally, these films can only be adhered to specific substrate materials, making them difficult to separate. Natural deposition produces more uniform photonic crystal films, but the surfaces are prone to unevenness. Additionally, these films still adhere to the substrate material and forcibly separating them can cause the photonic crystal films to break. The magnetic field assisted method can not only make the Fe₃O₄@C nanoparticles arrange into bright structural colors in a short period of time, but also make the Fe₃O₄@C nanoparticles arrange into periodic ordered structures in the photocurable polyurethane acrylate. This prevents the photonic crystal from being exposed to the air, reducing interference from external factors and enhancing the stability of the photonic crystal. The resulting Fe₃O₄@C photonic crystal flexible composite films are uniform in thickness and smooth on the surface. Ultrasonic treatment of Fe₃O₄@C nanoparticles is essential to obtain bright structural colors. Only the Fe₃O₄@C nanoparticles which have been ultrasonic treated to remove surface impurities can be arranged into periodic ordered structures with the help of magnetic field to display structural colors. Magnetic field assisted method can reduce the preparation time of the photonic crystal flexible film to some extent. The photonic crystal flexible composite film prepared by the magnetic field assisted method is more uniform and smooth, which also improves the stability of photonic crystal. It is helpful to promote the application of photonic crystal in security anti-counterfeiting, camouflage coating, sensors, solar cells, biomedicine and other fields.