High-efficiency, high-power density power converters have high requirements for magnetic components. In this paper, a four-phase integrated magnetic structure for LLC resonant converter is introduced, which integrates transformers and resonant inductors in a single core, reducing the volume of the magnetic core components. The magnetic is connected in series on the primary side and in parallel on the secondary side. The operation of series input and parallel output can effectively reduce the current stress of the rectifier. The winding design approach follows the magnetic flux cancellation, reducing core losses. The design process of the Integrated Magnetic is given a detailed description. Based on this, an optimization method is proposed to improve the power density and efficiency of the integrated magnetic. The feasibility of the proposed magnetic and optimization methods has been verified by simulation.