Abstract: Weft elastic silk fabric is a kind of parachute fabric. Due to the diversification of air impact load, the size of the fabric changed. As a result, the volume of air permeability changed. In the parameters of the properties of the parachute silk, the air permeability is an important parameter. According to the requirements of the air permeability performance of the parachute fabric, 15 types of weft elastic parachute silk, different outsourcing twist and different pre drafting ratio, have been designed. The relationships between the structure parameters of the fabrics have been researched, and the major factors impacting the air permeability of weft elastic silk fabric was found. It was found that the great warp density favors the small air permeability of the fabric. In addition, the air permeability of the fabric increased and decreased with the increase of the outsourcing twist. The air permeability of weft elastic parachute silk is the biggest when the outsourcing twist is 1000T/10cm.