The role of penetration and bond situation of cross-linking agents at different tanning stage on the apparent and thermal properties of sheepskin collagen fibre has been studied. The pickled sheepskins were tanned with basic chrome sulfate (BCS), ferrous sulfate (FS), mimosa-chrome sulfate (MCS) and mimosa-ferrous sulfate (MFS), and thermal stability of the modified fibres were researched using shrinkage temperature. The absorbing degree of crosslinking agents in the solvent were analysed by the variable trend of the agents' absorbancy with time. The results show that in the time range is 10 min to 120 min, the concentratiomn of crosslinking agents in the tanning solution would decrease with the increase of tanning time, and mimosa crosslinking agent is the most obvious. During the first 60 min, its absorptivity from tanning liquor can almost reach to 90%. The shrinkage temperature (Ts) reveals that thermal stability of modified collagen has been enhanced by the crosslinking agents. Ts of leather tanned with BCS, MCS and MFS were 98.6°C, 95.2°C and 108.9°C.