Abstract: In high-temperature gas-cooled reactors (HTGR), the motion of pebble flow within the core induces friction between graphite materials, inevitably generating graphite dust. This dust is carried out of the core by helium gas, circulates within the primary loop, and eventually deposits on primary circuit surfaces. Since graphite dust can potentially retain activated radioactive products, the migration of such radioactive dust poses a risk during reactor maintenance. Dust migration is governed by multiple physical phenomena. However, previous studies have predominantly focused on individual behaviors, which do not fully address practical engineering requirements. In this paper, the combined effects of coagulation, deposition, and convection processes of dust within the primary loop were investigated. Specifically, the discrete-sectional model was employed to accurately calculate the synergistic interactions between Brownian coagulation and thermophoretic coagulation. Multiple mechanisms were considered to evaluate deposition characteristics, and a system-level analysis based on the control volume model was conducted to establish a multi-behavior coupled analysis method for dust migration in the primary loop. A validation of the coagulation calculation method presented in this study was performed by utilizing the self-preserving distribution of aerosol Brownian coagulation in the closed system proposed by Vemury. The influence of thermophoresis on the total coagulation rate under different temperature gradients was analyzed. The dust convection analysis method in this study exhibits a high degree of agreement with the analytical solution of dust convection, validating the reliability of the proposed method. The multi-behavior coupling analysis method proposed in this study was comprehensively validated using the STORM deposition experiment. The total dust deposition obtained from the calculations is in good agreement with the experimental measurements. The method is applied to simulate changes in particle size distribution within hot gas duct. The results indicate that under full-power operation conditions of the HTR-10 helium duct, the obtained dust deposition rate distribution is in good agreement with the analytical solutions from the literature, validating the accuracy and engineering applicability of the proposed method in high-temperature gas-cooled reactor systems. Additionally, the results show that coagulation has a relatively minor impact on dust deposition within the inner tube of the helium duct.