In this study, the nylon copolymer was prepared by copolymerization reaction using polyetherdiamine and diacid, in addition add small amount of tri-functional compound to improve the resilience between molecular chains in which the molecular weight of polyetherdiamine is about 1000g*mol^(-1), the diacid is adipic acid , and the tri-functional compound is diethylenetriamine (DETA). The result showed that the polyetherdiamine providing good ductility, malleability and elasticity in nylon copolymer. Through the tri-functional compound can let copolymer increase amorphous region for molecular chains movement to enhance the intermolecular flexibility. The nylon copolymer elongation at break is up to 350%. In the melting spinning process, using Side-by-Side fiber structure by nylon copolymer and nylon, can make the recovery of elongation up to 90%.