Abstract: Driven by the "dual-carbon" goal and green manufacturing concept, the demand for lightweight applications of carbon fiber reinforced thermoplastic composites (CFRTP) is growing. Four types of double-layer stepped energy directors (ED) prepared using 3D printing technology were utilized for the ultrasonic welding of plain weave carbon fiber reinforced nylon 6 (CF/PA6), where the area of the lower layer of ED is slightly bigger than that of the welding overlap area, and the area of the upper layer is 100%, 64%, 36%, and 16% of the overall overlap area, respectively. The influence of the four types of ED on the joint quality was studied through tensile-shear test, metallographic microscopy analysis, fracture morphology observation, and welding process curves analysis. The results show that the size of ED structure significantly affects the performance of welded joints. The joint made with the 36% ED shows the best performance in terms of mechanical strength, interface fusion quality, and welding process stability. The lap shear strength of the joint reaches 28.9 MPa. This study validates the potential of 3D printed ED in the application of CFRTP ultrasonic welding, which provides new ideas for green and efficient joining technology.