A sample of multi-cladding high concentration silica host erbium doped fiber with bismuth-gallium-aluminum co-doped is fabricated by MCVD process with a type of annular graphite heater furnace. Its geometric parameters and absorption spectrum are measured and analyzed. It is presented that the mode field diameter and absorption coefficient of the erbium-doped fiber are both increased efficiently by using multi-cladding structure. The absorption reaches to 84 dB/m at 1530 nm and the mode field diameter is 11.6 μm at 1550 nm, but the background loss is 1.5 dB/m. An erbium-doped fiber amplifier is established and the best length of fiber is experimentally found. As a result, a 1.95 m C-band erbium-doped fiber amplifier is presented with small signal gain of 23 dB.