The utility model provides a one-step composite twisting machine, and belongs to the technical field of textile machinery. The unwinding device is arranged at the top of the first twisting spindle, sothat the problems of uneven yarn twist, fuzzing, bubbling and the like caused by unstable balloon tension in the yarn twisting process can be effectively solved. The one-step composite twisting machine comprises a first twisting mechanism, a roller transmission structure and a second twisting mechanism, in the primary twisting mechanism, monofilament twisting is conducted through a primary twisting spindle, two or more pieces of yarn obtained after monofilament twisting enter a roller transmission structure to be subjected to monofilament stranding, and stranded yarn is formed; the second twisting mechanism is used for compound twisting of the plied yarns; the unwinding device is arranged at the top of the primary twisting spindle, equivalently, a support is additionally arranged in the middle of a twisting area of yarn, the size of an air ring formed by the yarn in the twisting area due to high-speed rotation is fixed, the size of the air ring is basically consistent, and the yarn quality problem caused by collision with other parts is avoided. The problems of fuzzing, bubbling, many white points, many broken ends and the like of yarns of a traditional one-step twisting machine can be effectively solved.