The slow light propagation in optical fiber has attracted much attention because of its practical applications. Use of coherent population oscillation to produce slow light propagation has many advantages over other methods. We investigate the reduction of the group velocity propagation by the coherent population oscillation in erbium-doped optical fiber, and also the relationship between the population of metastable state and the time delay by changing the doping concentration, the length of the fiber, the input power, and the pump power. The results show that we can select a high doping concentration of erbium in the fiber, increase the length of the fiber, decrease the pump power and select the appropriate power of the signal light to increases the time delay.