Abstract: The outfield-induced resistance properties of Fe3O4/MgO(100) films were investigated. The Fe3O4 thin films were grown on MgO(100) substrates by laser molecular beam epitaxy (L-MBE). The Fe3O4 epitaxial film could be grown with the (200) face of MgO substrate as indicated by XRD analysis. The quality of the films was checked in situ by monitoring reflection high energy electron diffraction (RHEED) patterns and intensity oscillation during deposition. The results show that the film surface is plat, and the film growth mode is 2D layer-by-layer. AFM analysis reveals that the RMS roughness of the films is about 0.201 nm, which shows that the film surface is plat at atom level. The resistance of the films was investigated at the action of outfields such as magnetic field, temperature field and laser field. The results show that, the resistance of the films decreases generally as the temperature increases, while it has a peak at 120 K (known as the Verwey transition temperature), showing the films electrical character of semiconductor type. The resistance of the films decreases with laser field in the temperature range of 50-300 K, so the films show an instantaneously photoconductive character. The Verwey transition temperature is at 120 K for the laser off, but it ascends to 140 K for the laser on. The photoinduced resistance (PR) change increases with the temperature declining, which is due to the field-induced delocalization of charge ordered states in the films.