The experiment of pulsed laser welding with filler wire on 0.5 mm thick Hastelloy C-276 sheets is conducted, and the influence rules of laser single pulse energy and defocusing on the weld joint forming are studied. The study results show that the single pulse energy and the defocusing mainly influence the heat input of pulsed laser welding, spot size and spatial distribution of laser beam, and they also have a great influence on the macroscopic morphology of the weld joint forming. With the increase of the heat input, both of the top and bottom welding widths of weld joints increase, and the bottom reinforcement and the bottom contact angle of weld joints also increase. In a certain range of defocusing, the larger the laser spot diameter is, the wider the weld joint width is. With the influence of the laser beam spatial distribution, the top welding width is always slightly larger than the bottom welding width when the defocusing is negative. Under a certain process condition, the weld joints with controllable positive reinforcement, and the weld joint appearance with uniform weld width, reinforcement and contact angle, but small weld width, can be obtained. The top and bottom surfaces of weld joints are smooth and uniform, which show a feature of semicircular wave stripes.