The basic method and numerical schemes of pseudo-spectral diagnostic model is discussed for the global and limited area in this paqer. A numerical scheme of vertical integration of continuity equation is presented here to generalize two common used schemes, i.e. so-called "upward integration" method and "downward integration" method. The method presented in this paper has a high accuracy and a low requirement to the computer. It is also applicable to a global as well as a limited area.