This paper describes a simulation package for a power system using objected-oriented programming. The package includes four parts which are a power flow, a short circuit calculation, a transient simulation program, and an economic dispatch. The graphical user interface(GUI) is designed as a common platform which allows the user to create one-line diagrams of systems, specify components of power systems as well as simulation parameters, and view the output produced by the chosen application. The paper presents the data structure of the functional modules such as the draw module, power system data module, the power system simulation module, and the utility module using the object oriented programming. This package may be useful for educational and research purposes.