Experimental study on high power fiber laser deep-penetration welding of automobile 5052 aluminum alloy in an overlap configuration is carried out,and the main influencing factors on fiber laser welding are analyzed,and the micro-structure and the mechanical properties of the welded joints are measured. Through analyzing fiber laser welding performance of automobile aluminum alloy,the influencing factors such as fiber core diameter,gap thickness between two plates,kinds of shielding gas,and the protection way on the morphology and properties of overlap-welded joint are prominent. High welding speed and narrow weld pool and heat affected zone (HAZ) can be obtained when welding by fiber laser. Under the proper welding condition,the weld topography of top surface and bottom surface is even and continuous. Micro-hardness in fusion zone is higher than that of base material. The tensile-strength of welding joints is higher than its shear strength. The fracture is happened in HAZ and its topography is a mixture of ductile fracture as main mode and brittle fracture as subsidiary mode.