To obtain excellent performance optical fiber couplers,the structural difference of SiO2 in couplers under different manufacturing technique was investigated with 740 FT-IR micro infrared spectrometer.The infrared absorption spectra of SiO2 in couplers fabricated at different drawing velocities was measured. Two characteristic peaks in 650-2000 cm^-1 are observed.One characteristic peak is at about 943 cm^-1, which attributes to Si-O-Si bond asymmetric stretching vibration, the other is at about 773 cm^-1, which attributes to Si-O-Si bond symmetric stretching vibration. From the infrared spectrum,it is found that the characteristic peaks changes while the manufacturing technique is different. And the changing amount is measured.It is concluded that the asymmetric vibration of Si-O-Si is stronger in the glass of fiber coupler,and the wavenumber shift is the most important to the performance of the optical fiber couplers.