The development of polyamide fibers with excellent mechanical performance is always a hot research topic. In this paper, the structure evolution of polyamide 1212 (PA1212) after stretching at different temperatures was characterized by Wide-Angle X-ray Diffraction (WAXD) and Small-Angle X-ray Scattering (SAXS) techniques. Experimentally, it was found that there existed a maximum tensile strength of PA1212 after pre-stretching at 140 degrees C according to the subsequent mechanical measurements. The formation mechanism of this mechanical property variation was investigated from the different aspects of aggregation structure, such as crystal forms, degree of crystal orientation, crystallinities, density of micro cavity and lamellar long spacing. The related characterization results showed that the a from crystals, the highest degree of crystal orientation and crystallinities, and a lower density of micro cavity were formed when PA1212 was pre-stretched at 140 degrees C, which were crucial in improving mechanical properties of PA1212. The structure evolution from spherulites to oriented fibrils was observed directly from the images of scanning electron microscopy (SEM), and was also evidenced by 2D-SAXS and 2D-WAXD patterns. These findings expounded the structure evolution and formation mechanism of PA1212 fibers with excellent mechanical performance. (C) 2017 Published by Elsevier Ltd.