Thermal degradation of polyphenylene sulfide (PPS) film was investigated in air, nitrogen, helium, and argon with different physical and reactive characteristics from room temperature to 790degreesC by a high-resolution thermogravimetry (TG) at a variable heating rate in response to the changes in the sample's weight-loss rate. In nitrogen and argon, only a single-step degradation process of the PPS was observed, but in helium, a two-step degradation process of PPS was found. Notably, in air a four-step degradation process of the PPS, which was hardly ever revealed by a traditional TG, was found in this investigation. The initial thermal degradation temperature T-d and temperature at the first maximum weight-loss rate T-dm1 of the PPS increased in the following order: in helium < in nitrogen < in argon < in air. The first maximum weight-loss rate also increased with the variation of atmosphere in the order: nitrogen < air < argon < helium. The char yield at 700degreesC increased in the order: in air < in helium < in nitrogen < in argon. The activation energy of the major degradation process of PPS calculated based on the high-resolution TG data was very high, increasing in the order: in nitrogen < in argon < in helium < in air. The thermal decomposition parameters of the PPS determined by the high-resolution TG were systematically compared with those by traditional TG at a constant heating rate.