After the three-roll planetary rotary rolling of copper tube billet, there is an uneven phenomenon in the axial wall thickness of tube billet, which affects the wall thickness uniformity of tube billet by joint drawing. Therefore, in response to this problem, based on the principle of ultrasonic testing, a new type of online ultrasonic testing equipment after rolling was developed independently, and the online measurement experiment for the wall thickness of TP2 copper tube was conducted. Then, based on these experiments, a geometric model of copper tube billet by joint drawing was established by experimental data. Furthermore, the finite element simulation was used to analyze the influence of different joint drawing processes on the wall thickness uniformity of copper tube after joint drawing, and an evaluation formula for the axial wall thickness uniformity of copper tube was established. The research results indicate that the unevenness of initial tube wall thickness increases the fluctuation of drawing force during the drawing process and increases the distance of axial displacement of core head. Appropriately increasing the wall thickness reduction rate can improve the unevenness of axial wall thickness for copper tube after the moving core head is drawn. As the wall thickness reduction rate increases, the fluctuations in radial stress and displacement of moving core head during the drawing process become greater, which has guiding and reference significance for regulating the axial wall thickness uniformity of tubes in the drawing process of moving core head.