Sellmeier dispersion formula and Lorentz-Lorenz function are two common formulas that describe the relationship between the refractive index of materials and the wavelength of the incoming light wave at different temperatures. To examine the differences between the calculation results based on these two formulas, two theoretical models are used to simulate the refractive index, group index, group velocity dispersion (GVD), and the third order dispersion (TOD) of distilled water within the wavelength range of 400～1100 nm at four different temperatures respectively. The differences between the calculated results are analyzed. It is shown that the difference between refractive index and group index is rather small, but the differences in GVD and TOD can be relatively large.