This study quantitatively analyzes the load-relief behavior of the dentiform wall in the integrated support system of prefabricated pile curtains, to provide theoretical insights for the design and calculation of this novel composite support technology. Based on the load-relief mechanism of the dentiform wall in integrated support system with precast pile walls, and assuming the slip surface follows a rotating-wheel model, a calculation method is proposed to estimate the load-relief effect of the dentiform wall during soil slip behind the wall. This method utilizes the methodology of horizontal thin-layer differentiation. Additionally, the study examines the impacts of key factors—including the dentiform wall’s geometric parameters, soil strength, and soil-wall interface strength—on the load-relief effect, and validates the findings through numerical case studies. The proposed calculation method effectively addresses the challenge of quantitatively analyzing the load-relief effect of the dentiform wall in precast pile curtain supports. The results demonstrate that the dentiform wall significantly reduces the soil pressure behind the wall, achieving a load reduction ratio of up to 50%. Moreover, increasing the width of the dentiform wall significantly enhances the load reduction effect, while decreasing the spacing between dentiform walls also improves this effect; in contrast, increasing the wall thickness had less effect on reducing the load. The addition of a dentiform wall significantly enhances the support performance in high-strength soils. Furthermore, strengthening the soil-wall interface significantly increases the load reduction ratio, with interface cohesion playing a dominant role in enhancing this effect.