Abstract: Spatial augmented reality(SAR),which typically uses projectors to augment physical spaces with virtual contents,is one of the three main forms of augmented reality.In SAR systems,users can interact with virtual contents in physical spaces,therefore they have good environmental,spatial and collaborative perceptions.SAR systems can also reduce the cognitive load of interaction tasks.SAR display forms are firstly demonstrated,and then SAR architectures are illustrated as well as its technical principles.SAR interaction technologies are classified into 6 categories,which are touch based interaction,gesture or posture based interaction,3D controller based interaction,handholding projector interaction,tangible interaction,and multimodal interaction.Challenges from 3D registration,virtual-real fusion are analyzed.The application status in the field of sports,medical treatment,education,entertainment and art are discussed.The trends in SAR interaction are finally predicted.Specifically,SAR interaction will become more natural,more intelligent in occlusion processing,more widely applicable,more closely related with the social,cultural and psychological researches,and novel display approaches will also be used by SAR systems.