The work aims to evaluate a series of properties of secondary collagen fiber extracted from waste leather, especially the sound-absorbing and flame-retardant properties and explore the possibility of application of secondary collagen fiber and its composite yarn and cloth in packaging field. The secondary collagen fiber was tested by SEM, amino acid analyzer, Fourier transform infrared spectroscopy, standing wave tube method and oxygen index method. The mechanical properties of composite yarn and cloth were tested by universal tension machine. The secondary collagen fiber had porous and multi-layer structure. The best sound absorption coefficient was 0.98 and the limiting oxygen index was 34.7%. The secondary collagen fiber composite yarn and cloth had good mechanical properties. Therefore, secondary collagen fiber has good sound-absorbing and flame-retardant properties, and its composite yarn and cloth have good mechanical properties, which has a good prospect in packaging application.