In software projects it is crucial to control the actual project schedule, cost and product quality, against the project plan. Variations often occur during the running project, and big ones might have significant impacts on the whole project. Thus, it is necessary to identify causes quickly, and take the right corrective actions in time. This paper provides a threedimensional software development model, called AHA (Activity-Human-Artifact). It combines three key factors, activity, human and artifact, corresponding to project schedule, cost, and product quality, respectively. We also define some relevant elements, attributes and relationships among different dimensions in the AHA model, and their impacts with respect to schedule, cost and quality. On the basis of our model, a project tracking process is developed to guide analysts to locate potential causes for different kinds of variations, and effectively correct them in real projects. We also take a software project as the application scenario to illustrate our model and the tracking process identified.