In this paper, based on the electro-elastic surface/interface theory, the size-dependent effect on the torsional buckling behavior of functionally graded (FG) cylindrical nano-shell covered with piezoelectric nano-layers is studied. According to the classical shell theory together with von-Karman-Donnell type kinematics of nonlinearity, the primary formulations are given. The total energy of the nano-shell is derived by introducing the constitute relations for piezoelectric surfaces and interfaces. The principle of minimum potential energy is employed to establish the governing differential equations. An analytical solution is firstly presented, and then the generalized differential quadrature (GDQ) method is used to obtain the numerical results of nano-shells with different boundary conditions. Afterwards, the results without surface/interface effect are compared with the datum in the open literatures, and some numerical examples are presented to investigate the effect of surface/interface parameters and power-law index on the critical buckling load of the nano-shell.