We present a simple approach that could help quantitative phase field simulation for dilute-alloy solidification. The proposed approach mends the solute trapping problem by using a simple interface model (SIM), which requires only one free parameter. To test the feasibility of this model, a free dendritic growth from a small nucleus is simulated, and a good agreement with the anti-trapping current (ATC) model [Karma, Phys. Rev. Lett. 87 (2001) 115701] is obtained. By further studying the solute trapping effect during directional solidification, we find that the results give, with this model, a good thermodynamic consistence without solute trapping over two-order increment of the solidification speed and the interface thickness. Good agreement with the classical theory is obtained as well. (c) 2005 Elsevier B.V. All rights reserved.