The invention discloses a single winding device for an automatic soft bobbin winder. The single winding device comprises a winder, a variable-amplitude filament guide device, a fixed length control device, a tension adjusting device and a single-chip microcomputer, wherein the winder comprises a winding frame and a groove drum, the variable-amplitude filament guide device comprises a variable-amplitude guide rail, a tension spring, a movable pull rod and an adjustable rotary rod, the fixed length control device comprises an infrared light-operated filament detector, a thread shear, an alarm indicator lamp and a reset button, and the single-chip microcomputer is used for controlling all the devices. The single winding device is simple in structure, reasonable in design and low in cost and noise, pineapple-shaped forming and fixed length and broken filament automatic stopping functions can be conveniently realized in use of the single winding device, high-quality soft winding can be realized, dyeing quality in subsequent procedure and smoothness in rewinding can be improved, and accordingly operating efficiency and economic efficiency of factories can be improved.