In this paper, we propose a new model for software projects and an estimation method for the quality, cost and delivery date.The new model consists of Project model and Process model.Project model focuses on three key components: activity, product and developer of the project.Process model includes a set of Activity models, each of which specifies design, coding, review, test, and debug activities respectively using GSPN.Moreover, the new model can take the influence of human factors into account by introducing the concept of "workload".Next, we develop a simulator which supports description of the target process, executes the process described by Activity model and analyses the simulation results statistically.Then, we apply the simulator to real software projects at certain organization and compare the estimated values with actual data.The experimental results show the applicability of the proposed simulator to manage real software project in the future.