Phase shifter is one of basic integrated optical structures, and wavelength dependence of its phase shift value determines operation wavelength range of devices. An experimental investigation was conducted on silica-based integrated optical phase shifter designed respectively in two different regimes, length difference regime (LDR) and refractive index difference regime (RIDR), aiming at wavelength dependence of phase shifter. Phase shifters of 180° were respectively designed in the two regimes and inserted between two interference arms of Mach-Zehnder interferometers(MZI). Based on these two structures, a quantitative comparison on phase shift wavelength dependence was made by measuring wavelength dependence of MZI insertion loss. Experimental results show that the operation wavelength range of phase shifters designed in the RIDR was approximately 1.8-1.9 times that designed in the LDR. Analysis shows that the experimental results are in agreement with the theoretical calculations, which proves that phase shifter designed in RIDR possesses weaker wavelength dependence and thus wider operation wavelength range.