This paper aims at 3D interaction task analysis and construction, summarizes interaction tasks in 3D interaction field, presents the integration process from basic interaction tasks to universal interaction tasks in 3D/VR application, and finally constructs a core toolkit which can be widely used in 3D interaction field. This core toolkit specifies the low level structure of 3D interaction. A set of interaction primitives, interaction tasks and the process about primitive creation and task integration are defined in it. It can be used as the low level platform in 3D UI toolkit, 3D UIMS or 3D/VR application development. Therefore programmer can just pay attention to the high level work such as interaction style construction.