Quantification of root system architecture is essential for determining nutrient uptake by plant roots. Growing in opaque soils, roots are difficult to observe and interpret. This makes simulation modeling an attractive complementary approach. In this paper, root architecture models were reviewed and methods for constructing geometric models were introduced. SIMROOT, an important model for root architecture, was described as related to nutrient acquisition. By employing Extensible Tree data structure implemented on a SGI computer, this model provides vivid graphical visualization of root growing. Furthermore, the model can be developed to evaluate uptake of diffusive nutrients by plants. The application of these models was introduced. Modifications of the model to simulate competition for nutrient uptake within and between roots were also discussed.