When using normalized dispersion method for the dispersion design of photonic crystal fibers (PCFs), it is vital that the group velocity dispersion of PCF can be seen as the sum of geometrical dispersion and material dispersion. However, the error induced by this way of calculation will deteriorate the final results. Taking 5 ps/(km·nm) and 5% as absolute error and relative error limits, respectively, the structure parameter boundaries of PCFs about when separating total dispersion into geometrical and material components is valid are provided for wavelength shorter than 1700 nm. By using these two criteria together, it is adequate to evaluate the simulated dispersion of PCFs when normalized dispersion method is employed.