In order to solve the problems of poor utilization of powder and nozzle blocked by rebounded powder by improving the powder gathering characteristic and increasing the powder focal length, the influence of the cone ring gap and the cone angle of the coaxial nozzle on the powder convergence is studied. The results show that the powder gathering characteristic is better when the cone ring gap is smaller and the nozzle focal length is longer when the cone angle is bigger with other process parameters invariable. The conclusion is valuable for the coaxial nozzle designing and performance improving．The simulation results are verified by experiments. The effects of process parameters on the height and width of the single-trace are studied. The thin wall parts are manufactured by optimizing the process parameters.