Abstract: On the base of the electron-hole theory stated by Freund et al， this paper attempts to deduce and interpret the energy of the obvious lithosphere-atmosphere-ionosphere coupling observed on May 9， 2008， three days before the Wenchuan M_S8.0 earthquake. During the process， we set the largest horizontal principal stress and the earthquake plate area of the main fault. The simulation results show， during the period of the micro-cracks developing into the macro-cracks before the main rupture occurs， the total surface charge range of the main fault falls in 10⁶—10⁷ C and the related upward electric field， which is perpendicular to the interface between the Earth surface and the atmosphere， is 10⁷—10⁸ V/m. The corresponding parameters are up to 10⁸ C and 10⁹ V/m when the main rupture happens， and the output current is up to 10⁵ A in order. On one hand， the electric field increasing in the interface between the Earth surface and the atmosphere， can cause electromagnetic parameter abnormities of the ground-based observation， with the range beyond 1000 km; on the other hand， it can accumulate air ionization above pre-earthquake zone， leading to ionospheric parameters short-time sudden changes recorded by some spatial seismic monitoring satellites.