Based on the rate equations and light propagation equations of homogeneously broadened four-level system, the numerical simulations for tellurite-based optical fiber amplifiers (EDTFA) are presented in the paper. Effects of energy transfer between Er3+ levels due to cooperative up-conversion, cross-relaxation, excited state absorption and background losses are considered here. The theoretical simulation results show a good agreement with the published experimental results. Further more, the relations between the amplifier gain and the input signal power, bi-directional pump power, and the fiber length are simulated numerically.