The combination of the double-cladding fiber laser and the periodically poled material provides a compact and high efficiency approach for wavelength conversion with high beam quality. Green laser source is demonstrated using a combination of laser-diode-seeded Yb-doped double-cladding fiber laser and quasi-phase-matched second harmonic generation in periodically poled lithium niobate (PPLN). The uncoated 20-mm-long, 5-mm-wide, 0.5-mm-thick PPLN has 6.5 μm poling period and is temperature stabilized at 193.1℃. The 6.7% conversion efficiency and the 59 mW green light power are achieved with the pump fundamental average power of 650 mW and 970 mW, respectively.