The aim of present research is evaluatio of impact resistance for commonly used weft knitted fabrics. High-strength fabrics are often used in ballistic impact protection systems where ?exibility and lightweight are of importance. When a projectile impacts a fabric, a force is exerted on the projectile by the fabric, which reduces its velocity. At the same time, the fabric is deformed. Strain waves originating from the impact region propagate along yarns toward the fabric edges, where they are re?ected. otherwise The structure of weft knitted fabrics is related to stitch elements and stitch density which affect on fabric mechanical properties. improvement of mechanical properties in the through-the thickness direction, Knitted fabrics are one of the textile fabrics that are gaining interest, because of the excellent drapability of knitted fabric and hence the possibilities for near-net-shape- manufacture of ?bre preforms. As ?bres in knitted structures are oriented not only in the in-plane directions, but also in the thickness direction, the through-the-thickness properties of knitted fabrics are highest among unidirectional ?ber. To find the optimized structure of fabric, various samples of weft knitted fabric have been produced in different pattern and densities and mechanical properties for whole samples have been measured specially strength, work u rupture and impact resistance in course and wale directions. The experiments have demonstrated that structures of more knit elements could resist against slow impacts and they might have more work of rupture. Also, it has been found that fabrics with structures of more skip elements could resist against sharp impacts. Artificial neural networks (A) are information processing mechanisms that consist of a large number of densely interconnected simple computational elements, which have been studied for many years in the hope of achieving human-brain-like performance in a digital computer . The back propagatio neural network (BPANN) has been used to predict the mechanical properties of nylon 6.6 weft knitted fabrics based on fabric structure as fitne functio using in genetic algorithm. The genetic algorithm (GA) have been applied to fined optimum fabrics according to structural parameters. Genetic algorithms are adaptive methods which may be used to solve search and optimization problems. They are based on the genetic processes of biological organisms.G.As use a direct analogy of natural behavior. They work with a population of individuals each representing a possible soulution to a given problem.finally, The results have been shown that the optimum fabric could be made with more ski elements in structure, lower loop length and more compact density. Key words : Optimization, impact, weft knitting, Genetic Algorithm