FexMo1-xS2 with an expanded interlayer spacing of 0.75 nm was prepared via a simple solvothermal method. The larger interlayer spacing enhances the rate of Na+ diffusion during initial cycle. FexMo1-xS2 as an anode for sodium ion batteries exhibits a high capacity of 285 mA·h/g at 0.1 A/g after 100 cycles and an excellent rate capability of 178 mA·h/g at 5 A/g. The fresh and cycled electrodes were characterized by in-situ X-ray photoelectric spectroscopy and transmission electronic microscopy to investigate electrochemical reaction mechanism of FexMo1-xS2 during cycling. The results indicate that the irreversible conversion reaction of FexMo1-xS2 with Na+ results in the formation of main products of Fe-Mo alloy and S.