Based on retaining the excellent properties of nylon-6 (PA6), nylon-6/66 copolymers (PA6/66) with well-controlled dimensional stability and toughness exhibit more potential applications. In this work, PA6/66 random copolymers were synthesized by melt copolymerization of epsilon-caprolactam and hexamethylene adipamide salt. The sequence distribution, crystal morphology, crystal forms, and melting and crystallization behavior of PA6/66 copolymers were systematically investigated by quantitative C-13 NMR, polarized optical microscopy, wide-angle X-ray diffraction, and differential scanning calorimetry, respectively. The crystallization activation energy increases from -286.43 to -212.43 kJ mol(-1) as the co-polyamide bond ratio increases from 0 to 0.22, while the deteriorating sequence regularity does not alter the original crystal morphology and crystal forms of PA6. Significantly, control over the crystallization behavior of PA6/66 copolymer has been obtained through finely regulating its sequence distribution. This work could provide theoretical support and new insights for controllable preparation of PA6 copolymers and ultimately be beneficial to extend their applications.