High-concentration erbium-doped fiber plays a very important role in optical transmission and related devices based optical-fiber. On the grounds of characteristic of modified MCVD technique, the preforms were manufactured by "online" solution doping technique. The fabrication process of Er3+-Bi3+-Ga3+-Al3+ codoped fiber by using modified furnace round heating MCVD was discussed. Especially, the depositing temperature of porous core layer was very significant, the best value was 1560 ℃～1600 ℃. The action mechanism of bismuth was also discussed. The effect of increasing concentration of Er3+ by codoped Bi3+, Ga3+ and Al3+ was analyzed. The core areas performances were detected by scanning electron microscope (SEM) and the mole ratio of different ingredients of fabricated fibers were measured by electro-probe micro analyzer (EPMA). The highest absorption coefficient at 1530 nm was about 60 dB/m. The concentration of Er3+ in the fiber was about 3.84×1025 m-3.