Abstract: A BNCT treating planning system MCDB is developed.Three-dimensional material matrix and tally matrix are designed, which are used to describe voxel models and tally.A fast track technique is used in simulation.Computation time is greatly decreased compared with MCNP code.Same dosimetry results with MCNP are achieved by MCDB,which is faster by 3.1-3.4 times with respect to MCNP.Computation time and accuracy of most voxels reach clinical BNCT requirement in a scale of 10 million particles.