<p>Recent studies have identified radial cracks in post and beam supports in timber structures, but there is a lack of systematic studies on the effect of cracks on burning behavior. In this study, the burning behavior of timber specimens with inclination angles of 0°, 15°, 30° and 45° and varying cross-section widths was investigated. The analysis of flame patterns, temperature profiles, the mass loss rate and charring degree showed that cracks had a significant effect on the combustion behavior of wood. The mass loss rate (MLR) was higher for wood with radial cracks compared to wood without cracks. By introducing the concept of charring volume and assessing the effect of cracks based on charring length and depth, it can be seen that cracks have the greatest effect on the area directly exposed to the flame. The effect of cracks increases dramatically when the angle reaches 30°. Cracks affect combustion through two main mechanisms: firstly, external heating accelerates the airflow at the crack, creating an entrainment effect that increases the oxygen content in the combustion zone; secondly, the accelerated airflow enhances thermal convection. This study provides a comprehensive analysis of the effect of cracks on combustion behavior and provides a reference for the restoration of timber-framed buildings.</p>