A model of power limit of hundred-nanosecond single-frequency pulsed fiber lasers established, by which the maximum extractable power of ytterbium-doped silica fiber and phosphate fiber are analysed. Numerical results show that the power of Yb3+-doped silica fiber sources is limited by pump brightness, lens effect and stimulated Brillouin scattering (SBS), while, for Yb3+-doped phosphate fiber sources, melt of the core is also included. On the aspect of maximum extractable power of single-frequency pulsed laser, phosphate fiber is better than silica fiber.