Abstract: Four types of powder tubes made of aluminum (6061), titanium (TA1), stainless steel (304), and copper (H62) were selected. By controlling the length and inner wall roughness of the powder tubes, the powder outflow pattern was photographed using a DSLR camera to measure the divergence angle. The differences in divergence angles among powder tubes made of different materials with the same length, as well as the changes in divergence angles of powder tubes made of the same material with different lengths and surface treatments (smooth or rough), were analyzed. The results indicate that the powder tube material has a negligible effect on the powder divergence angle; increasing the powder tube length can reduce the divergence angle, but it tends to stabilize once it exceeds a critical threshold; an increase of the roughness of inner wall of the powder tube significantly enhances the collision dissipation effect between the powders and the tube wall, leading to an increase in the divergence angle. The powder divergence angle is determined by the ratio of the lateral velocity to the longitudinal velocity of the powder. The powder tube length regulates the divergence angle by affecting the attenuation of the lateral velocity, while the turbulence induced by the roughness of the inner wall is a key factor in increasing the divergence angle.