Electromagnetic boundary conditions (EMBCs) are theoretical fundamentals to  describe electromagnetic behavior in electromagnetism, optics, condensed matter  and other physical branches. Traditional EMBCs were derived based on the abrupt  flat interface model. The abrupt interface model ignores intrinsic sizes of electrons  and transition of the electromagnetic field across the interface, which makes it  unable to explain spill-out effects and photoexcitation of interface electrons and  scattering of light near Brewster angle. Moreover, the flat interface model is directly  used to study the scattering of nanoscale metal spheres, ignoring the influence of  interface curvature on electromagnetic boundary conditions, which makes it difficult  to accurately predict the frequency shift of the absorption peak of nanoscale plasma.  In order to better study the optical phenomena induced by these nanoscale interfaces,  it is necessary to construct nanoscale EMBCs and develop nanoscale  electromagnetic theory. In this thesis, the nanoscale EMBCs are constructed for both  the infinite plane and nanoscale curved surfaces. Transition of electromagnetic field  on the interfaces is described by the four interface response functions (IRFs) and  IRF-tailored novel optical phenomena are further explored.        On macroscopic plane surfaces, generalized nanoscale EMBCs are derived  with IRFs representing the field inhomogeneity across the interface based on integral  Maxwell’s equations. On this basis, the equivalent interface dipole moment model  and the equivalent polarization (magnetization) charge and current model are  constructed, and the corresponding boundary conditions are given. Then, based on  the nanoscale EMBCs, the Fresnel formulas containing IRFs are derived. It is found  that IRFs have an obvious regulation effect on the Brewster angular position and its  reflection coefficient. The phenomena of non-extinction, continuous phase change  and adjustable Goos-Ha?nchen shift induced by IRFs are observed. In the case of  total reflection and metal strong reflection, additional absorption or enhancement  effects induced by the imaginary part of IRFs are observed. These unique optical  phenomena induced by the interface not only enrich the physical connotation of  interface-regulated photon behavior, but also provide a new idea for the  measurement of IRFs.         Based on the study of macroscopic plane surfaces，the influence of the rotation  of local coordinate system on electromagnetic field is further considered. Nanoscale  EMBCs suitable for nanoscale curved surfaces are deduced based on the surface  model with transition layers. Based on these EMBCs, the absorption coefficient of  nanoscale metal spheres is given, and the absorption spectrum regulated by IRFs is  obtained. With the decrease of the radius of the metal sphere, the phenomenon of red  shift or blue shift of the resonance frequency of the localized surface plasma (LSP)  is related to IRFs, which provides a possible explanation for the uncertainty of the  absorption peak frequency shift of LSP shown in previous experiments. The results  provide a necessary theoretical basis for accurately regulating the light field on the  nanoscale.