In order to obtain high efficient SHG- in fibers, a new method of two-stage laser preparation was used to prepare Er8+ doped silica fibers. The maximum peak power conversion efficiency measured was 8.8%. The length dependence of frequency-doubled light in Br3+-doped silica fibers was studied, and the mechanism of high efficient SHG in Er3+ dopod silica fibers was discussed. The experimental results showed that the pulss width of SH light is 0.7 times as long as that of IB light and that the 8H power is qnadratically dependent on the IR power in short fibers,and confirmed that the SH light is generated through a second-order nonlinear process.