This study aims to model and analyze the thermo mechanical buckling behavior of honeycomb core sandwich nanoplates. The analysis is conducted using a new high-order shear deformation theory and nonlocal strain gradient elasticity theory, considering the thickness strain effect. The sandwich nanoplate, resting on a viscoelastic base, consists of a honeycomb structure in the inner layer and symmetric surface layers made of functionally graded material. It is subjected to thermal and magnetic fields. The core layer is made of biocompatible SUS304 stainless steel, while the surface layers are made of zirconium on the outside and SUS304 on the inside. The equations of motion for the sandwich nanoplate are derived by incorporating the thermal forces, Lorentz force, and the fundamental forces from the spring and shear basis into the equations. Hamilton's principle is used to obtain these equations and then solved using the Navier method. An in-depth analysis is conducted on the effects of parameters such as inclination angle, length ratio, and thickness ratio on the thermal buckling behavior of the sandwich nanoplate. In addition, the effects of surface layer material composition, temperature rise, external horizontal magnetic field, nonlocal effects and viscoelastic fundamental parameters are comprehensively studied. The thermal buckling behavior of sandwich nanoplate can be favorably modified by careful tuning of honeycomb parameters, material properties of surface layers, magnetic field intensity and viscoelastic fundamental parameters.