Ancient Chinese timber buildings featuring the Dougong system are renowned for their structural resilience, with the Dou component playing a key role in transferring vertical compressive loads and ensuring stability. However, field investigations have revealed that Dou components are vulnerable to damage under vertical loading. This study investigates the crack behavior of Dou components under vertical compression using Digital Image Correlation (DIC). Twelve full-scale Douglas Fir specimens, based on historical geometries, were tested under displacement control while surface strain evolution was captured in real time. Results reveal three typical crack modes: extension of original cracks, X-shaped cracks, and growth ring separations. Extension of the original cracks showed strain localization around the existing crack already in the elastic stage, while the other two modes emerged during yield and plastic stages. Crack patterns were found to evolve in a sequential and coupled manner, ultimately leading to failure zones. DIC effectively traced crack initiation, propagation, and interaction, providing quantitative insights into mechanical deterioration processes. The correlation between crack behavior and load stages enhances understanding of progressive damage in wood components. These findings demonstrate the potential of DIC in capturing crack evolution under controlled loading, providing valuable insights to support the structural assessment and conservation of timber heritage structures.