Abstract: In the spinning process of pneumatic compact spinning with lattice apron, the existence of a wrap twisting phenomenon has been approved via high-speed photography technology. The additional twists in the fiber strand in the condensing zone, which are considered to be real twists, are also approved to exist through yarn spinning experiment. Based on these results, a ‘semi-open-end twist insertion’ model is proposed. The model can well explain the formation mechanism of the additional twists in the fiber strand in the condensing zone of the pneumatic compact spinning and enriches the yarn spinning theory.