The coupling vibration performances of axisymmetric piezoelectric circular nanoplates under thermo-electro-mechanical fields are studied based on the nonlocal strain gradient theory and Mindlin plate theory. Hamilton’s principle is used to develop the equations of motion in the framework of nonlocal strain gradient constitutive relations，and the differential quadrature method is adopted to solve differential equations describing the theoretical model. The influences of internal scale parameters and external field parameters on natural frequencies of piezoelectric circular nanoplates are analyzed. It shows that the natural frequency of piezoelectric circular nanoplate decreases with an increase of the nonlocal parameter，and increases with an increase of the strain gradient characteristic parameter. When the nonlocal parameter is less than the strain gradient characteristic parameter，the circular nanoplate demonstrates a hardening behavior. When the nonlocal parameter is greater than the strain gradient characteristic parameter，it demonstrates a softening behavior. When the nonlocal parameter is equal to the strain gradient characteristic parameter，the stiffness degenerates into the corresponding result of classical continuum theory. Additionally，it indicates that the natural frequencies decrease with an increase of the radial compressive load and positive voltage，and increase with an increase of the radial tensile load and negative voltage. The natural frequency decreases slightly with an increase of the temperature. In particular，it is found that while increasing the radial load and voltage to a certain value，the vibration instability occurs. The effects of the nonlocal parameter and strain gradient characteristic parameter on the critical radial load and critical voltage are analyzed accordingly.