The concept and method of full-dimensional(F-D)observation of distribution system security region(DSSR)are proposed. Firstly

on the basis of summarizing the shortcomings of the existing 2D and 3D projective observation method

the concept of F-D observation is put forward. Secondly

the F-D observation method based on the security distance is proposed

which includes the following contents: (1)The equivalent radiuses of DSSR are defined as the distance from original point(zero loading point)to all of the effective security boundaries; (2)The DSSR radiuses are visualized by line and radar map to observe the characteristics and concavity of DSSR; (3)The concavity indices and the shape distortion index are defined to quantify the degree of concavity and distortion of DSSR; (4)The reasons of concavity and the solutions to solve the concavity problem are acquired by analyzing the concavity security boundaries expressions. Finally

the proposed F-D observation method is illustrated and compared with 2D/3D projective approach through the case studies. The result shows that the F-D method can achieve complete observation of high dimensional regions and detect the hidden defects which 2D/3D method is difficult to find. The new F-D method provides a powerful tool to explore the deeper information in DSSR.