Fiber optic communication based all-digital channel has been widely applied in power system protection. The appearance of digital channel technology makes all kinds of information exchange reliable and fast， then the construction of unified pilot protection system（UPPS） is becoming possible. Based on abundant wide-area synchronous real-time information， UPPS can not only apply several protection criteria to improve performance of relay-protection system， but also implement some auxiliary functions.So it is in favor of increasing reliability of relay-protection system further. Finally， the technical background， relay-protection intelligent electronic device（IED） structure， information frame classification and format of UPPS are introduced. Besides， UPPS functions and implementation principle such as relay-protection performance improvement， auto-reclosure coordination， transmission line parameter on-line calculation and volt-ampere characteristic measurement and calculation of transient resistance are discussed.