Abstract: In spatial augmented reality(SAR)systems supporting tangible interaction,user interactions can cause rapid changes in orientation and position of interaction objects.To ensure the efficiency and accuracy of registration during objects movements,a digital twin registration technique for SAR is proposed.Models are made in the digital space and their geometric parameters are entirely consistent with the objects in the physical space.The orientation and position parameters of the physical objects are tracked in real-time during user interaction.Then the digital objects are adjusted according the parameters.Moreover,intrinsic and extrinsic parameters of the projector,which are calibrated in advance,are used to set the virtual camera in the digital space.The projection patterns are rendered in that virtual camera and then projected onto the interaction objects.The efficiency and accuracy are evaluated in the middle school physical experiment learning magnetic induction line based on the projection interaction tabletop,which meet the requirements of tangible interaction in SAR systems.