The layout of the buckets for tunnel boring machine (TBM) directly affects the muck removal efficiency of cutterhead during excavation. In order to improve the muck removal performance for TBM, the optimal design of bucket layout was investigated. The whole muck transfer process was simulated by discrete-element method (DEM), including the muck falling, colliding, pilling up, shoveling and transferring into the hopper. The muck model was established based on size distribution analysis of muck samples from the water-supply tunnel project in Jilin Province, China. Then, the influence of the bucket number and the interval angle between buckets on muck removal performance was investigated. The results indicated that, as the number of buckets increased from four to eight, the removed muck increased by 29% and the residual volume decreased by 40.5%, and the process became steadier. Different interval angles between buckets were corresponding to different removed muck irregularly, but the residual muck number increased generally with the angles. The optimal layout of buckets for the cutterhead in this tunnel project was obtained based on the simulation results, and the muck removal performance of the TBM was verified by the actual data in the engineering construction.