An integrated structure of passive elements in an LLC resonance converter realized by flexible circuit boards includes a closed magnetic circuit formed by first and second magnetic cores, a tubular, double-sided, flexible circuit board, tubular magnetic-material layer and tubular, single-sided, flexible circuit board. The single-sided circuit board is coaxially sleeved in turn from inside outwards on a magnetic core column of the closed magnetic circuit. The tubular, double-sided, circuit board is a laminated plate material formed in turn of a first insulating layer, first copper foil, insulating medium layer, second copper foil and second insulating layer. The tubular, single-sided, circuit board is a laminated plate material formed in turn of a third insulating layer, third copper foil and fourth insulating layer. The integration of a resonance capacitor, resonance inductor, shunt inductor and transformer in a LLC resonance converter is realized by using these flexible circuit boards.