Abstract: The object oriented technology in direct digital control systems was studied. A direct digital control system that is industrial nucleon balance measurement and monitor system was designed and developed. Three level modul structure was built, and object oriented programming method was adopted in all of the submodules, such as system configuration, real time control, and so on. The disadvantages in the generality, flexibility, and maintainability of process oriented programming were overcomed. The application prospect of the system was good.