Abstract: The geometrical structure of magnetic field in the magnetosphere is an important issue for discussion in space physics. In this paper an analysis has been made to some regions of magnetosphere, including the Nightside, Cusp and Duskside. By applying the Curvature Radius Method to the magnetic field data measured by four satellites of Cluster, the geometrical structure of Magnetic Field Lines, including the curvature radius, directions of curvature and normal of the osculating planes of the Magnetic Field Lines have been investigated. Then the spacial configuration of Magnetic Field Lines is known ,and consequently the three dimensional structures of the corresponding regions are achieved according to the anterior results. And finally the results testified the validity of the Curvature Radius Method. If more detailed datas are supplied, a three-dimentional model of the whole magnetosphere can be built by extending the method to the other regions in magnetosphere. So the significance of the research is very clear for space science.