Pointing at the problem of the all-reflection Fourier transform spectrometer that its ability of weak light detection is wasted, we has carried a further structure on the original Fresnel double-sided mirror structure. The former coupled Fresnel double-sided mirror is separated for a distance. Meanwhile, move the two separated plane mirror up for a proper distance around the optical axis. The improved structure’s interference field is just distributed above the optical axis which was used to around the axis of symmetry and its upper and lower was symmetry. Simulations results show that the further structure’s incident light energy’s utilization rate and the interference fringe Fourier transform’s resolution are doubled. The improvement has important significance to enhance the all-reflection Fourier transform imaging spectrometer‘s weak light detection capability and expand its spectrum detection range.