In order to solve the image rotation in Sagnac transverse shearing interferometer, a model system is built on ray vector tracing and rotation matrix theory, as well as the theoretical imaging orientation and the actual imaging orientation with the angle error are demonstrated. Besides, the relation between the angle error and the rotation of the image body is concluded, which provides a theoretical guidance for optical alignment in Sagnac transverse shearing interferometer. Finally, an optimized optical alignment scheme is provided by the discussion of the angle error in the assembly and system-level loading process, which is also validated by optical alignment instance. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.