The load paths play a crucial role in expressing the transfer of internal loads within a structure from a global perspective. This understanding is highly significant for optimizing and designing structures. However, existing methods face challenges in visualizing load paths for complex three-dimensional structures and evaluating their load-bearing performance. In this article, we propose a novel evaluation index, based on load path density, to effectively express and assess the mechanical performance of such structures. To begin with, we introduce a calculation approach for load paths, utilizing the force equilibrium principle. We also define a new evaluation index, denoted as load flow capacity ( S), which quantifies the density of load paths. Furthermore, we study the load path density within the same load flow channel to validate the accuracy and applicability of the derived load flow capacity. Additionally, we compare and analyze the disparities between load flow capacity and Von-Mises stress. Finally, we apply this evaluation index to a case study involving a pillow bracket. Through this study, we unveil the internal load transfer mechanism and evaluate the load-bearing performance of the bracket. The findings from This research provide valuable insights for engineers in the design and optimization of structures.