The invention relates to an all optical fiber low repetition frequency parametric oscillator used for stimulated Raman scattering. Pump light output by a pump source passes through an isolator and a first optical coupler to enter a parametric oscillation cavity; combined waves of the first and second optical couplers enter a gain optical fiber and a parametric conversion medium; the gain optical fiber amplifies the pump light power of the parametric oscillation cavity entering from the first optical coupler; the output light of the gain optical fiber enters the parametric conversion medium which is in direct fusion with the gain optical fiber; a four-wave mixing effect occurs in the parametric conversion medium; and one part of the output light of the gain optical fiber is directly output,and the other part of the output light of the gain optical fiber returns to the first optical coupler as feedback light, so that the parametric oscillation cavity can be formed. The optical couplersare placed at front of the gain optical fiber so that the gain optical fiber and the parametric conversion medium can be in direct fusion, and therefore, that optical coupler tail fiber generates harmful non-linear effects under low repetition frequency and high peak power pump light can be avoided, parametric conversion efficiency can be enhanced, frequency spectrum noise can be reduced, and theall optical fiber low repetition frequency parametric oscillator can be realized.