An on-orbit composite filament forming device for space 3D printing, comprising a constant tension unwinding module, a replaceable resin filament rotary wrapping module, a melt preheating chamber, a curved channel impregnation chamber, a variable aperture resin recovery device, a heat protective housing, a convective cooling device, a traction device, and a winding device arranged sequentially, wherein the melt preheating chamber, the curved channel impregnation chamber, and the variable aperture resin recovery device are located in the heat protective housing;
- the replaceable resin filament rotary wrapping module comprises at least one active unwinding reel placed on a circular rail centered on a carbon fiber;
- a first metal scraper opening and closing mechanism, a second metal scraper opening and closing mechanism, and a third metal scraper opening and closing mechanism are provided sequentially inside the variable aperture resin recovery device;
- a circumferential heating resistor is provided in a housing of the variable aperture resin recovery device, and a lateral push device is provided at an upper part of the housing.