Abstract: The creep behavior of spandex core-spun yarns which were spun with soybean protein fiber,cotton or polyester fibers as outer sheath was tested.On the basis of viscoelasticity theory of textile material,four element mechanics model was utilized to analyze the extensional deformation rule of spandex core-spun yarn.Using DPS data processing system,the fitted equation of creep elongation was developed.The creep behavior of soybean-spandex,cotton-spandex and polyester-spandex core-spun yarns was studied accordingly.The results revealed that the creep behavior of spandex core-spun yarn varies with the fiber used as outer sheath,and the theoretical calculated value agrees well with the practical results.Four element mechanics model is ideal for describing the creep law of spandex core-spun yarn.