The energy band and lattice structures of trigoqal Se and Te are calculated by the vector charge density wave (VCDW) model. A little simplified VCDW modeUs formulated using theCNDO-UHF approximation. The VCDW model with a suitable parametrization is shown to explain the geometry, XPS and optical gap data. The Fermi surface of the cubic P band is shown to have a nesting structure responsible to produce the VCDW. The band dispersion of trigonal Se and Te is mainly determined by the dispersion of the cubic P bands that correspond to the prototype lattice structure of the trigonal crystal. The VCDW produces gaps and splits the metallic cubic P bands into three subbands. The lattice distortion by the electron-lattice coupling, the nearest neighbor exchange interaction and the intraatomicCoulomb repulsion additively contribute to the gaps. The lattice distortion is proportional to the bond order modulation of the VCDW. The contribution of the nearest neighbor exchange int~raction to the gaps is also proportional to it, while that of the intraatomic Coulomb repulsion is proportional to the P electron density modulation of the VCDW.