An idea about structure of unified pilot protection system is proposed. By virtue of optical fiber communication system， it can obtain multi-information such as sample values of analog current， voltage and all kinds of digital information. With these information， it can not only accomplish many criterions in one protection system to enhance the performances of pilot protection system， but also achieve some other auxiliary functions such as re-closure coordination， line parameters calculation and so on. Based on the idea， fault direction information is used to overcome problem that differential protection is easily influenced by current transformer properties difference and current transformer saturation. In addition， a detailed analysis of current transformer saturation effect on performances of current differential component and positive sequence fault direction component is given. The results show that limited influence on fault direction component caused by current transformer saturation， so it can detect fault direction reliably and provide auxiliary information for current differential protection to distinguish internal fault from external one， accordingly， the corresponding protection criterion is put forward. The results of dynamic simulation experiments verify the feasibility and effectiveness of the proposed scheme.