Photonic spin Hall effect (PSHE) of light, similar to the spin Hall effect of an electronic system, is the interaction between photon spin-orbit of spin splitting phenomenon in refractive index gradient field. PSHE provides a new way to manipulate photons and accurately measure relevant physical effects. This paper studies the photon spin splitting in the magneto-optic Kerr effect, and establishes the quantitative relationship between the magneto-optical Kerr rotation and the PSHE. We have observed the magneto-optic Kerr effect of the action of an iron film in the magnetic field. After finishing experiments, we firstly analyze the amplified shift of the spin changing with the magnetic intensity in the case of horizontal polarization and vertical polarization incidence. Then, the Kerr rotations changing with the incident angle for different magnetizations are measured separately. Finally, comparing the above two results, we obtain that the accurate magneto-optic Kerr rotation angle is 6.7×10-5o/μm. If the position sensor based on phase-locked amplifier (20 nm) is used to measure the magneto-optic Kerr rotation angle, its precision can be improved by one or two orders of magnitude. These results prove that the PSHE not only can be used to accurately measure the magneto-optic Kerr effect, but also have great significance in magnetic film research. Especially, in terms of magnetic-optic devices, PSHE can be used to achieve the superior performance of endurance cycling and data retention.