Because of the absorption of erbium-doped optical fiber, the group velocity of the optical pulse propagation is slowed down and the intensity of signal is reduced, which brings more difficulties to the actual measurement of slow light and its application in communications, such as the distortion and the low measurement.Therefore only after the group velocity slowdown of light pulse in erbium-doped optical fiber under no absorption loss is realized, can the slow light technology really have the practical application. We investigate the erbium-doped optical fiber amplifier deeply and develop a technology, in which the different pump powers and fiber lengths are used to reduce the signal loss through theoretical calculation and realize the group velocity slowdown of light pulse. The results show that no absorption loss is realized at a pump power of 3.5 mW, and we realize the slow light with a fiber length of 0.1 m when the pump power is zero.