Both the Horowitz-Metzger method and Coats-Redferm method were employed to get the thermal degradation activation energy (TDAE) of the samples. With the changes in thermal degradation activation energy of the samples processed with urea solutions being considered, the influence and mechanism of urea processing on the aggregation structure of collagen fibers were discussed. It was found that, with the increase in urea concentration, the thermal degradation activation energy first decreases and then increases. After being processed in urea solutions, the samples were washed with distilled water to remove the urea, and the thermal degradation behaviour of the samples was also studied. It was found that the thermal degradation activation energy recovers to its original level, indicating that the urea function on collagen fibers is temporary and reversible. The mechanism of urea processing involves the destruction of hydrogen bonds between collagen chains. Upon water washing, the urea was removed from the samples, and the collagen structure returned to their origin al state.