A wavelength-spacing tunable multi-wavelength fiber optical parametric oscillator (MW-FOPO) with a simple line cavity is proposed. A tunable laser provides the pump seed light. A pseudorandom modulation method is used to broaden the line-width of the pump seed light by employing a phase modulator, which can successfully suppress the stimulated Brillouin scattering (SBS) when the high power pump light is injected into the highly nonlinear optical fiber(HNLF). A high power erbium-doped fiber amplifier is used to achieve a high power pump source. Stable multi-wavelength lasing at room temperature is achieved due to the four wave maxing (FWM) effect and the broadband gain of the fiber optical parametric amplifier. The wavelength spacing of the MW-FOPO can be tuned by adjusting the wavelength of the pump light. Seventeen lasing lines with an extinction ratios larger than 10 dB which cover the wavelength region from 1505 to 1615 nm are achieved. Advantages of fiber optical parametric amplifiers to implement multi-wavelength fiber laser are demonstrated.