The traditional LLC resonant converter is analyzed by using the fundamental analysis method (FHA), which ignores the influence of high-order harmonics on the circuit and results in significant gain errors when deviating from the resonant point. In this paper, the time-domain analysis method (TDA) is used to draw the gain surface of the LLC resonant converter, as well as the surface of the inductance ratio and quality factor. A group of resonant parameters are designed. At the same time, a magnetic integration technology is adopted to integrate the resonant inductor and transformer into one magnetic core. The optimal selection of loss and volume for the integrated magnetic components is carried out, and shielding layer technology is used to reduce the influence of parasitic parameters on the primary and secondary sides of the converter at high frequencies. According to the finite element simulation results, the integrated magnetic components reduces losses by 33% compared to discrete magnetic components, and the power density increases by 43.8%. Finally, a LLC resonant converter with a power of 800 W, a switching frequency of 1 MHz, and a voltage of 400 V/48 V is built, and the rationality of the resonant parameters and integrated magnetic component design is verified through experimental testing results.