The Early Tang Dynasty caissons at the Mogao Grottoes in Dunhuang possess highly complex structures and rigorous visual order. Existing research has largely focused on style and symbolism, lacking systematic, verifiable, and quantitative analysis. Guided by iconography and Gestalt theory of visual perception, this study proposes a six-dimensional coding framework: core motif, number of border layers, canopy elements, color gradation, the presence of the Baoxianghua (precious flower) motif, and compositional symmetry. Manual coding of 24 well-preserved Early Tang Dynasty caissons, combined with thematic analysis and inductive methods, reveals several key characteristics of this phase: a strengthened core, simplified borders, and weakened canopy; predominantly axial and radial compositions, with a few exhibiting mirror symmetry; a transition from intense contrast to gradual layering and gradation; and a significant increase in the frequency and spatial extent of the Baoxianghua motif. This framework provides reusable evidence for structural and perceptual research on caissons, advancing not only quantitative research and digital preservation but also methodological support for the translation and application of Dunhuang motifs in contemporary design.