CT tube is the core component of CT equipment. CT tube adopts dynamic magnetic focusing technology to facilitate the realization of small focus when there is large current output. Flying focal spot technology can record each projection of each scan from multiple angles, improve the sampling rate, and greatly improve the image definition and quality. CST software is used to simulate the CT tube based on dynamic magnetic focusing. When the CT tube outputs high current of 1 A, the key parameters of the dual magnetic quadrupole lens are optimized to get the target size of focus of 0.2 mm×0.6 mm and the function of flying focus.