Nanowires,nanofibers and nanotubes have been widely used as the building blocks in micro/nano-electromechanical systems,energy harvesting or storage devices,and small-scaled measurement equipment.We report that the surface effects of these nanobeams have a great impact on their deflection and inteal forces.A simply supported nanobeam is taken as an example.For the displacement and shear force of the nanobeam,its dangerous sections are different from those predicted by the conventional beam theory,but for the bending moment,the dangerous section is the same.Moreover,the values of these three quantities for the nanobeam are all distinct from those calculated from the conventional beam model.These analyses shed new light on the stiffness and strength check of nanobeams,which are beneficial to engineer new-types of nano-materials and nano-devices.