We systematically investigated the L-edge X-ray emission spectroscopy (XES), a 3d-to-2p transition, of Fe2+- and Fe3+-bearing MgSiO3 perovskite under high pressure based on the internally consistent LSDA+U technique combined with the Slater-transition method. The Fe L-edge XES spectra can be used to directly interpolate the distribution of Fe-3d electrons including the spin states and coordination environments of iron. Our results show that the spin transition from the high-spin state to low-spin state of Fe2+ and Fe3+ can be identified easily by the L-edge XES technique. The valence state of Fe (2+ or 3+) can be verified by this, since a shift of the first main peak of Fe2+ across the spin transition of 2 eV, in good agreement with the experimental value (~1.6 eV), is significantly smaller than that of Fe3+ of 4 eV. The width of the L-edge XES of Fe3+ also depends strongly on the substitution sites (Mg or Si), meaning that its coordination environments might also be distinguishable based on the Fe L-edge XES spectra. These strong sensitivities to the Fe’s states suggest that the high-resolution Fe L-edge XES would be a useful experimental technique to investigate Fe-bearing silicate minerals.