Abstract: The numerical analyzing about the influence factors on limiting the output power of erbium doped fiber laser, considering the nonlinear effect, the thermal effect and the facet damage as well as combining the single mode condition, the single mode erbium doped fiber laser was simulated to get a maximum extractable power of 6.34 kW operating at 1 570 nm. Besides, in less mode condition, maximum extractable power of the erbium doped fiber laser can reached 53.39 kW. The limited output power in single frequency condition was simulated and the results show that in absolutely single frequency condition, the power limit of erbium doped fiber laser was 245 W. At last, the fact working condition was analyzed and the promoting methods of power was focused on. As results, decreasing the core numerical aperture (NA) and promoting the beam quality in less mode condition can be effective ways to gain the limited output power.