The temperature-dependent structural changes in 1-butyl-3-methylimidazolium tetrafluoride ([Bmim]FeCl4) magnetic ionic liquid (MIL) were investigated by using in-situ X-ray absorption fine structure (XAFS) combined with Raman spectroscopy and DFT calculations. XAFS results revealed that the coordination number and bond length of Fe-Cl in the anion of [Bmim]FeCl4 MIL decreased with increments in temperature. These results directly reflected the dissociation of tetrahedral structure [FeCl4]-, and the formation of bridge-chain [Fe2Cl5]+, and [FeCl2]+species in the anion of [Bmim]FeCl4 MIL. These behaviors indicated that [FeCl4]- dissociation was endothermic, and was promoted by increased temperature. The results obtained through XAFS were in agreement with those obtained through Raman spectroscopy and DFT calculations.