With the development of power technology and the demand of power user for higher reliability,small current grounding system has been the main neutral grounding method of distribution power grid.Single phase ground fault line detection has been one problem with medium distribution power grid relay protection in small current system.This paper presents small current fault line detection algorithm based on extensive and profound achievements by researcher from home and broad in this field in recent years.Analyses of the algorithms' advantages and disadvantages is also performed.The difficulty and direction of research in the future are discussed.