According to the theory of quasi-phase-matching (QPM), the periodical domain structure in gadolinium molybdate crystal for QPM second harmonic generation is designed. The designed domain period is 5.54 μm if the fundamental wavelength is 1.064 μm. The periodical domain structure is fabricated via poling the crystal with applied external pulse field. The switching time t c of the crystal is 500～600 μs when the external field is 2.5 kV/mm. The periodical domain structure has been obtained under the conditions that the voltage is 2.5 kV/mm and the duration of the applied pulse is 0.6～0.8t c. Using the periodically poled sample, harmonic wave of 0.532 μm has been achieved when the power of the fundamental Nd∶YAG laser is 7～10 W.