Group velocity of the optical pulse propagation would be reduced based on coherent population oscillation effect in an absorbing medium. According to the absorption properties of erbium-doped optical fiber, there would appear a sharp absorption loss, which brought more difficulties to the actual measurement of slow light and its application in communications. From the ground rate equation of erbium-ion, the delay of optical pulse was simulated under controllable absorption loss， and experiments were implemented to verify the theoretical results. Moreover, we researched how the different pump power and fiber length effect the signal loss and the optical pulse delay.