Laser scanning welding experiment and simulation study were carried out for 7075-T6 aluminum alloy 10 mm medium thickness plate. The inhibition law of laser scanning welding on weld porosity was investigated by X-ray nondestructive testing and molten pool flow simulation. Experimental results show that the porosity decreases with the increase of scanning frequency and amplitude. By analyzing the simulation results at different scanning frequencies, it is found that the "large keyhole" structure is more stable and less likely to collapse and form bubbles due to the superposition of keyholes at high frequency scanning, compared with the slender keyhole at low frequency scanning. At the same time, the beam scanning increases the width of molten pool and the probability of bubbles escaping. By analyzing the simulation results under different scanning amplitudes, it is found that the large amplitude significantly reduces the depth of the keyhole, which reduces the aspect ratio of the keyhole and enhances the stability of the keyhole. At the same time, the increase of amplitude further expands the width of the molten pool, which increases the probability of bubble escape and then reduces the porosity in the weld.