The holes were drilled by femtosecond laser pulse (800 nm, 100 fs) on Cu sheets at different ambient pressures. The pressure range was from 1 Pa to atmospheric pressure. The number of pulses to drill through the target, the stable photodiode signal, and the hole diameter were obtained as functions of ambient pressure. The morphology of the hole was observed by a scanning electron microscope (SEM). The result showed that the ambient pressure had significant influence on the morphology of the hole.