In order to improve the extrusion effect of nozzle structure in 3D printer, investigate the different influences of the extrusion effect resulted from the shrink by the shapes of curve and cone. By researching the construction of nozzles in the 3D printer with plunger piston, using the CFD technology to provide statistics and images and designing different nozzle curves, compare the results from pressure, velocity distribution and expansion with the help of Polyflow. It turns out that using the curve-shaped flow channel with lager shrinking rate in the design of nozzles will improve the intensity and accuracy of the work piece made of gunpowder.