Abstract: To address the lack of reasonable structural solutions and optimized design methods for the mucking of two-stage cutterhead of existing full-face rock tunnel boring machines (TBMs), this study constructs a numerical model using the particle discrete element method to simulate the mucking process of two-stage cutterhead of TBMs,so as to verify the reliability of the numerical model through scaled mucking tests. Numerical simulations are carried out to investigate the influence of various factors, including mucking outlet arrangement and size, spiral form and pitch, diameter ratio of primary/secondary cutterheads, and cutterhead rotation speed, on the performance of mucking. The results show that the spiral structure is an effective structural solution for mucking of TBM two-stage cutterhead, and the impact degree of each factor on the integrated mucking performance of two-stage cutterhead is, in descending order, cutterhead roation speed > length of back outlet of the primary-stage cutterhead > rear spiral pitch.For a two-stage spiral cutterhead with a tunnelling diameter of 8 m, the optimal structural form and parameters are recommended to be: the face and back muck outlets are in the same position with front and rear spirals, and specifically, the rear spiral pitch should be 0.85 m, the back muck outlet of the primary-stage cutterhead should be 0.9 m long, the diameter ratio of the primary/secondary-stage cutterhead should be no more than 0.55, and the cutterhead rotation speed should not exceed 6 r/min.