The phase field modeling (PFM) has emerged as a powerful tool for the simulation of the solidification of polycrystalline alloys. The use of the diffusive interface in PFM allows the treatment of the complicated morphology. However, in dealing with the grain boundary diffusion, it is difficult to simulate the diffusion process that is independent of the interface thickness. To amend this, we propose a model that imbeds a grain boundary diffusion term in the existing adaptive phase field model. In this new model, the simulated solute transport is independent of the interface thickness, and the simulated grain boundary diffusion is in good agreement with the classic solution. Crown Copyright (c) 2010 Published by Elsevier B.V. All rights reserved.