Abstract Thin film is the form of material that most closely resembles the silicon-based integrated circuits (IC) and therefore has attracted tremendous attention over the past decades due to its potential applications in integrating functional devices on IC chips. The structural characterization of thin films, especially epitaxial film with complex structure has been a long-term challenge until the emergence of synchrotron three-dimensional diffraction technique (3D-RSM). 3D-RSM is a technique that can effectively collect various structural information of epitaxial films, such as crystal lattice, strain, domain variants, and oxygen octahedral rotation. Now, interpreting the massive experimental data of 3D-RSM becomes the biggest obstacle that is confronted by the researchers. In this work, we proposed a strategy that utilizes simulated 3D-RSM diffraction patterns as aid of data analysis. With this approach, the one-to-one correspondence between diffraction spots and domain variants, as well as the quantitative lattice constants and crystal system have been identified in sequence for two typical cases, either epitaxial PbTiO3/SmScO3(001) film or (CoCrFeMnNi)3O4 alloy film epitaxially grown on LaAlO3(001) substrate. Further, systematic simulations of 3D-RSM patterns for epitaxial films belonging to every of the seven crystalline symmetries were performed and exhibited, assuming the films are grown on a (001)-oriented cubic substrate. This work sheds light on more effective data analysis of 3D-RSM, i.e., more effective structural characterization of complex epitaxial films.