Abstract: This paper descibes all nearest-neighbors relations of feature submatrices in fault verification techniques with a Voronoi hypersphere, analyses deveation disturbance angles between the feature submatrices and an unitary basis submatrix of the -dimension maximal orientation-energy subspace of a measured voltgage-change matrix through disturbance theories. Based on the above, the paper proposes novel diagnosibility theories for the system of fault verification techniques, derives a necessary and sufficient diagnosability condition in verification techniques for analog fault diagnosis under toralence disturbance. In addition, the paper classifies diagnosis problems with the revealed diagnossability.