In this work, femtosecond laser drilling process of nickelbased single crystal alloy DD6 was studied. The aperture, taper and roundness error of film cooling holes in DD6 alloy under different femtosecond laser process factors, including defocusing amount and pulse energy, were characterized by SEM. Experimental results demonstrate that when the defocusing amount deviates from 0 either to the positive or the negative direction, taper and upper aperture of the holes increase, but lower aperture decreases. With the focus moving from the inside (positive) to the outside (negative) of the sample, the roundness error gradually increases. With larger single pulse energy, the diameter as well as roundness error become larger and the taper becomes smaller. When the defocusing amount is 0, the taper of the holes processed by femtosecond laser with 100μJ pulses energy after machining 30min is the best.