Abstract: The focal length of the powder stream and the spatial distribution of the powder particles at the focal position are two key characteristics of the powder beam, which have a greater impact on the characteristics of the laser coaxial powder feeding additive manufacturing process. Using high-speed photography to capture the macro morphology of the powder beam, based on the image gray-scale processing technology, a method for characterizing the spatial concentration distribution of powder particles at the focal positions of the powder stream was established, and the effective powder spot diameter was used to quantitatively analyze the powder beam. The main process parameters such as carrier gas flow rates, coaxial shielding gas flow rates, and powder feeding rates have been systematically studied on the key characteristics of the powder beam. The research results show that the change of process parameters hardly affects the law that the spatial distribution of powder particles at the focal position of the powder stream is Gaussian. As the carrier gas flow increases, the focal length of the powder beam will be shorten, the effective powder spot diameter will become larger, and the flow convergence becomes worse. With increasing the coaxial shielding gas flow, the focal length of the powder stream becomes longer, and the effective powder spot diameter is almost unchanged. With the increase of powder feeding rates, the focal length of the powder stream and the effective powder spot diameter change little.