Many heat-treatable aluminum alloys are strengthened by the formation of coherent or semi-coherent precipitates during artificial aging treatment. We aim to build an aging model to predict the evolution of precipitate microstructure. In the present stage of this research we focus on simulating precipitation of plate-like strengthening phases, e.g. θ′ in Al-Cu alloys. The phase field method developed by Chen's group [1, 2] is adopted. The input parameters into the phase field model are mainly derived from thermodynamic and first principle calculations. The model also utilizes a few adjustable parameters such as the anisotropy of mobility coefficient, which can be determined by calibrating the model against experiments. Simulation results of precipitates in one-, two- and three-dimensions are shown in this paper. The model can reproduce the plate-like morphology of θ′ precipitates, simulate impingement of precipitates on different habit planes in the aluminum matrix, and also predict the characteristic low-peak-low variation of the aspect ratio of the precipitates during the growth and coarsening stages. Good agreement is found between the model and experiment.