The combination of periodic nonlinear polarization crystal and fiber laser is an effective technological mean to achieve visible and ultraviolet band laser output. In this paper, linearly polarized all-fiber laser oscillator is used as the pumping source, and single-pass, second harmonic generation in 5% (mole fraction) MgO doped periodically poled lithium niobate (PPMgO∶LN) nonlinear crystal is demonstrated. The temperature tuning characteristics are analyzed. Keeping the crystal temperature at 26.9 ℃, the green light output power of 1.437 W is achieved at the pump fundamental power of 8.05 W with the best harmonic efficiency of 17.84%.