In order to obtain a coaxial powder feeding nozzle matching a 3 kW broadband rectangular laser, the discrete phase model of Fluent software was used. Four factors and four levels of orthogonal simulation experiments were carried out to study the influence of the structural parameters on the concentration of the powder and the size of the powder spots. The results show that the powder concentration of the broadband coaxial powder feeding nozzle obeys the Gaussian distribution in the axial and radial directions, which verifies the rationality of the nozzle structure. The effects of the four factors on the powder concentration from large to small are: inclination angle, vertical height, contraction angle and outlet gap; when the optimal structural parameters are used, the nozzle can be formed a rectangular powder spot with a size of 3.08 mm×3.08 mm and a maximum density of 32.29 kg/m3 on a plane that 24.6 mm away from the powder outlet. In the end, the powder feeding experiment was carried out to verify its rationality, which provided a basis and reference for subsequent laser additive manufacturing experiments.