Targeting the gas-powder coupled transmission process of coaxial powder feeding laser cladding, an equivalent model is proposed to consider the influence of the complex collision behavior between the powder and nozzle wall and the powder on the exit angle and speed of the powder. In addition, the gas-powder transmission model outside the nozzle is established. Key variables, e.g., transient position of the powder, trajectory of motion, and average density of the continuous distribution of the powder, were simulated, and the influence of the surface state of the workpiece and flow rate of compressed gas on the above variables was studied. The results demonstrate that the simulation results are in good agreement with experimental results from the overall shape of the powder beam, gathering position, and track line density. The rebound of powder when the molten pool is not formed is more significant in the center of the powder beam (about 10 mm from the workpiece), the powder density in this area increased by approximately one times at the maximum, and as the height from the workpiece increased, the effect of increasing the powder density gradually weakened. The compressed gas flow rate increased to 2.5 m/s, the powder density on the central axis of the powder beam increased to approximately 5.2 kg/m³, the compressed gas flow rate continued to increase to 5.0 m/s, and powder density on the centerline was reduced by approximately 8%.