Abstract: Modulation is a key technology of a fiber laser.Without polarization control,the laser is unable to be modulated.With strictly polarization control,a novel structure of stabile fiber laser was set up.The fiber laser was made of a twisted normal and Er-doped fiber and could be modulated well.The modulated laser was already used in an over 100km single mode fiber fiber transmission system.The result is accordance with that of the transmission system by using semiconductor laser.