The quasi phase matched second harmonic generation in periodically poled lithium niobate (PPLN) Z cut 0.5 mm thick annealed proton exchanged (APE) waveguide with fan grating was realized by applying an external field poling. The grating period ranges inverted from 5.8 μm～6.2 μm and the interaction length was 4 mm. Used a CW Nd:YAG laser as a fundamental beam source at 1.064 μm, input power in waveguide was 10 mW. The green SHG of 20 μW at 0.532 μm was achieved at 125%/(W·cm 2) normalized conversion efficiency in PPLN waveguide.