Generally fiber lasers are classified as two types according to their principles. One is based on nonlinear effect of silica fiber, and the other is based on the simulated emission of rare earth ions which are doped in the optical fiber. the rare earth elements doped in the fiber are always lanthanide series. The development of femtosecond fiber laser is analyzed and the characterstics of several femtosecond fiber lasers are demonstrated. The idea to resolve the present problems of the femtosecond fiber lasers is gave.