Testwashbackhasattractedagooddealofattentionfromresearchersfrommanycountriesintheworldandconsiderableresultshavebeenfound.Bystudyingformerresearches,thispaperreviewsthedefinitionofwashback,relevantconcept,theories,andthemechanismofwashbacksystematically.Itishopedthatthispapercanenrichanddeepenthedevelopmentoflanguagetestingtheories.