Abstract: To design photonic crystal fibers (PCFs) in a less computational cost and time consumption way, it is better to use empirical relations method instead of other effective index methods. In this study, we intend to investigate both empirical relations method and modified fully vectorial effective index one to compare them with an accurate and powerful method like as full-vector finite element method. We found that empirical relations method has less error than the method of modified fully vectorial effective index in calculating PCFs parameters such as neff and the second order dispersion. In this study, we also calculate the third order dispersion by these methods. Finally, we will introduce the suitable method for designing PCFs among methods of empirical relations, fully vectorial effective index, modified fully vectorial effective index and scalar effective index.