Abstract: Horizontal injection technology was first introduced in early 1990s.It gets more mature after more than a decade of development and application.To get a thorough summary of the technology,the mechanism of the technology both at home and abroad,reservoir selection conditions,well pattern design,factors affecting water injection,and its on-site application are discussed.It has the advantages of long injection section,being capable of generating a lot of thermal fractures,and line drive.It can effectively increase water injection,reduce injection pressure,improve sweep efficiency.It is suitable for singe and double thin zones.Drilling and completion technologies as well as rational injection allocation are engineering factors that exert effect on water injection.Horizontal injection technology has been applied both at home and abroad.It is getting a favorable way to develop thin oil reservoirs with low permeability.