Fourier transformation (FT) method has been used in the theoretical lineshape analysis of the Franz-Keldysh Oscillation (FKO) in detail by numerical simulation. The FKO of a set of GaAs SIN+ samples was obtained in photoreflectanc e measurements.The FT spectra of a part of the samples,including of the real par t,imaginary part,and mode of the FT,are well consistent with the theoretical lin eshapes.The ratio of the square root of the reduced mass of the light hole (LH) to the heavy hole (HH),μl/μh,obtained in the analysis wa s in the range of 0805 to 0816 for different samples.In addition,the built-i n electric field Ｆ1,and the modulation field δＦ=F1-F2 induced by photo-modulation were also obtained in the analysis.However ,for a few samples great difference was found in the lineshape of the real part and imaginary part of their FT spectra from the theoretical lineshape.In this ca se the mode of the FT spectra still can be used to obtain useful information.