The dynamic process of generation, propagation and collapse of vapor channel induced by pulsed CO2 laser is monitored by a high speed camera. The influence of different defocus conditions on vapor channel is investigated. Sequence images of vapor channel process are captured, and coefficients that characterize vapor channel such as maximum depth are acquired. The results show that different defocus conditions have significant impact on kinetic process of vapor channel. Under pre-focus and focus plane conditions, the shape is similar to a funnel as the vapor channel propagates to the maximum depth, however, under the post-focus condition, the shape is similar to U. The experiment results provide reference for laser medicine, underwater laser processing and energy fields.