<p>The combined finite-discrete element method (FDEM) has been widely used to simulate the rock fracturing process. However, the penalty-based contact interaction algorithm commonly utilized in FDEM is element size-dependent, which may yield artificial non-smoothness and abrupt jump of contact force. Specifically, the amplitude and direction of the obtained contact force between two contacting blocks can vary even when their overlap area is unchanged. To circumvent the limitations, we establish a unified distance potential field using the boundary node lists to calculate contact forces and consider the update of the local distance potential field when new fractures are generated. The proposed algorithm not only ensures momentum and energy conservation but also avoids the dependence of contact force on element size, which is thus suitable for any complex cases. The effectiveness and robustness of the proposed method for contact interaction between discrete bodies are verified, and its advantages are demonstrated. Finally, we present two application examples to demonstrate the capability of the proposed approach for evaluating rock slope stabilities when multi-block contact is involved. The work provides a new effective solution to analyze discontinuous computation models associated with complex rock mass systems.</p>