Welding of 5083-H116 aluminum plate with thickness of 4 mm using IPG YLS-6000 fiber laser is presented. The influence of parameters on the weld forming and weld defects is carried out in this paper. Also, microstructure and mechanical properties of joint is analyzed. It indicates that laser power, speed and defocus have great effects on penetration state. The main problems of weld of 5083-H116 aluminum plate are sag and undercut. Under the condition of penetration, using high power of 5 kW and 6 kW and speed range from 6 m/min to 9 m/min can get ideal weld formation. With the optimal parameters of zero defocus, 6 kW power and 9 m/min welding speed, metallographic observations indicate that crystalline morphology near the fusion line is dense columnar, and in center of the weld which is isometric dendrite. Besides, the segregation of weld is more visible. The test shows that the micro-hardness of weld fluctuates and the mean value is less than the parent material. Tensile strength of joint is up to 287 MPa, about 83.9% of parent material. Yield strength is about 227 MPa. Elongation is about 3.57%. The tensile fracture happens in weld, and belongs to ductile fracture.