The invention relates to a high-power-density onboard variable voltage rectifier, which comprises an input connector, an input filter unit, a pulse transformator, a rectifying unit, an output filter unit, a heat radiation unit, a fault warning unit, an output connector and a casing, wherein the casing consists of a bottom plate, a panel and a cover hoop. Compared with an independent voltage stabilizing circuit, the high-power-density onboard variable voltage rectifier has the advantages that the device number is decreased, the system complexity is reduced, the system reliability is improved, and characteristics of low input current harmonic waves, stable output voltage and the like are realized. The high-power-density onboard variable voltage rectifier is suitable for being applied to middle-high-power rectifying occasions in aviation industry and national production.