Multiple input multiple output (MIMO) and pre-coder are the effective methods to overcome the influence of the time-varying channel since it is a key factor of the communication performance. However, the existing researches of MIMO and pre-coder focus on the spectrum efficiency under the Gaussian input assumption. This drawback limits the pre-coder technology application in the green communication. In order to overcome this shortage, we studies the energy efficiency of MIMO system in the time-varying channel based on the time-delay ability of the communication service under the equal probability finite-alphabet input assumption which is more likely to the digital communication signal. Furthermore, a feasible pre-coder algorithm based on the stochastic dynamic program is proposed. The numerical results show that the proposed algorithm performance approaches the energy efficient up bounder of the MIMO system effectively.