Abstract: Coaxial auxiliary gas blowing structure has important effect on the efficiency of deep hole machining by femtosecond laser, but there is poor effect of slag removal in the process. In order to improve the capacity of slag removal, ANSYS CFD software was used to simulate the distribution of flow field with coaxial gas blowing, paraxial gas blowing and double-channel gas blowing. Experimental platform of double-channel auxiliary gas blowing was designed. After theoretical analysis and experimental verification, the distribution of dynamic flow field and velocity vector of micropore inner and around the micropores were obtained. The hole morphologies were obtained after micropore treatment assisted by coaxial, paraxial and double-channel gas blowing structures. The results show that double-channel auxiliary gas blowing can not only improve processing efficiency but also help to clean the workpiece surface. It is of great significance to the realization of high efficiency deep hole processing by femtosecond laser.