Abstract: There are many micropores in shale, and the micropore structures can be exposed by Ar-ion milling technology. An Ar-ion beam was applied to treat a cross-section of shale with variable acceleration voltage, milling time, incidence angle and rotation speed of the sample holder. The milling effects were observed with a scanning electron microscope (SEM). The results show that appropriately lower voltage makes a smoother milling surface, and there is an optimal milling time. Meanwhile, a higher incidence angle and lower rotation speed of the holder can improve the milling effects.