To increase the spectrum resolution without changing the size of static Fourier interferometer, the bilateral-wedges Fourier transform interferometer was designed and the methods of stretching interference fringes in the same optical path difference were proposed. Through analyzing the optical path difference function between the bilateral-wedges Fourier transform interferometer and static Fourier transform interferometer, the spectrum resolution was enhanced to 9.1 cm-1 with the same size, and the enhancement was nearly 8 times. It will not bring about being unable to collect the interference fringes due to fringe aliasing. In the experiments, the bilateral-wedges Fourier transform interferometer was made by the BK7, using laser with six different wavelengths to show analysis of interference fringes. The experimental result demonstrated the interference fringes to be longer than normal with the augmentation of the reflection position. Of course, the kind of this error can be calibrated, because it is linear augmentation by wavelength. According to the calculation, it is known that each 1nm of the laser wavelength change causes 0.021 1 nm increase in the error. After the spectrum calibration, the system can detect the correct spectrum data, raising the spectrum resolution with the same size.