The invention discloses a mixed modulation isolation type three-circuit output DC-DC converter. The converter comprises an input power supply, a parallel full bridge LLC resonant circuit and a phase shifting full bridge circuit, wherein the parallel full bridge LLC resonant circuit converts a direct current input voltage into a high direct current output voltage by adopting a frequency modulationmode, and has a secondary side adopting a full wave rectifying circuit structure; the phase shifting full bridge circuit comprises a first branch and a second branch; the first branch is connected between any two bridge arms of the parallel full bridge LLC resonant circuit, and converts the direct current input voltage into a first low direct current output voltage by adjusting the phases betweenthe two bridge arms; the second branch is connected between the two residual bridge arms of the parallel full bridge LLC resonant circuit, and converts the direct current input voltage into the secondlow direct current output voltage by adjusting the phases between the two bridge arms; and the secondary side adopts the full wave rectifying circuit structure. The converter can realize mutual isolation of three circuits of output through two different control methods between the two bridge arms.