The effects of groove angle, focal length of lens and defocusing amount on the melting behavior of the materials in the grooves are studied by utilizing the fiber laser to scan and weld aluminum alloy V-grooves. The results show that the V-groove can focus fiber laser apparently, and the better melting effect in grooves can be obtained when the focal length is 300 mm, the defocusing amount is 0~10 mm, and the incident angle is 5°. Further analysis demonstrates that, this is attributed to the low absorptivity of aluminum to fiber laser at the Brewster angle. In addition, because of the energy losing for each laser reflection, the overmuch number of reflection of fiber laser in V-grooves is inappropriate.