The operation principle of distributed fiber Raman gain amplifier is discussed. The light amplification was obtained at 1410 nm wavelength region by using a 1320 nm solid laser as pumping source and a 23 km single mode GI optical fiber. The relation between the gain of fiber Raman amplifier and the effective interaction length of optical fiber is studied. When the pump peak power is 50 W and 30 W, the effective interaction length is 15.5 km and 10.5 km. The relation between the gain of Raman amplifier and pump power at different effective interaction length of optical fiber is anlyzed. The spectrum width of Raman fiber amplifier is estimated to be 50 nm or 250 cm from the Raman backscattering spectrum of optical fiber.