Abstract: pinning differential linear density and differential shrinkage filaments directly has great significance in the development of wool-like products.So to research and find out how the differential shrinkage filaments come into being in the same spinning process is also a meaningful work.In terms of a single screw extruder spinning,it can be assumed through theory discussion that the fine filaments are cooled faster with a smaller cooling length,and have a bigger drawing strain rate.The fresh formed fine filaments have a higher macromolecular degree of orientation and a higher boiled water shrinkage.But during the subsequent drawing the crystallization rate of the fine filaments is far higher than that of the coarse ones.So,the fine filaments can be imparted a high crystallinity and lower boiled water shrinkage.On the contrary,the coarse filaments turn into high shrinkage filaments.