Modern industrial application and technologies require materials with superior mechanical and thermal properties. Kevlar fibers have been known as fibrous materials with good properties of high strength and high decomposition temperature which have become a hot research field in recent years. The properties of fibrous materials depend on their structures and compositions. Thermal decomposition processing of the materials is of great significance for their structures and thermal properties. As a new technique, thermogravimetric (TG) analysis coupled with Fourier transform infrared spectroscopy(FTIR), are able to analyze materials not only qualitatively but also quantitatively. This method has obvious advantages in researching the thermal decomposition of many materials. However, the thermal decomposition processing of Kevlar fibers is rarely reported in the literature, therefore, we firstly studied the pyrolysis behavior of Kevlar fibers with thermogravimetric analysis coupled with Fourier transform infrared spectroscopy at the temperature of 30~800 ℃. We not only obtained the processing of the Kevlar fibers' thermal decomposition with great details but also the products of every stage. Experimental results exhibited that the decomposition of Kevlar fibers has experienced three stages： 100~240, 240~420 and 420~800 ℃. The weight loss of Kevlar fibers was quite slow before 500 ℃. The third stage was the main stage of the decomposition, and the amount of residue finally reached to a mass percent of 56.21%. FTIR analysis illustrated that free water released from Kevlar fibers at the first stage, followed by the dehydration and depolymerization which made polymer chains short. Finally the fiber fragments further reacted and produced the gases of small molecular mass, and the main products were water, ammonia, carbon monoxide and carbon dioxide. Generation rate of water was increased; the emission of ammonia was at the same rate; carbon monoxide was only produced at the temperature of 515~630 ℃, then turned into carbon dioxide. The release of carbon dioxide was on rise because of the conversion process of carbon monoxide, and then dropped to a certain value.