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A fine-long tube model was established for carrying out the thermal degradation experiments of steam foam to determine the foam stability in steam chamber. The real core sand from the Yulou oil layer of Block Jin45 of Liaohe Oilfield was packed in the model, and the experiment lasting for twenty days was conducted under the typical reservoir pressure and saturated steam temperature. The analysis on the experimental results and theoretical calculation results indicate that the thermal degradation reaction model of the added foam is the first-order reaction, and the degradation rate constants at the temperatures of 200 °C, 250 °C, and 300 °C are 9.35×10−8 s−1, 17.80×10−8 s−1, and 24.53×10−8 s−1 respectively. The foam thermal degradation rate kinetic model was deduced, which can be used to calculate the foam thermal degradation rate and half-life at any temperature condition. The half-lives of the added foam are 370 d, 160 d, 83 d, 49 d and 31 d at the temperatures of 100 °C, 150 °C, 200 °C, 250 °C and 300 °C respectively, which indicates that the production performance of most heavy oil reservoirs developed by steam drive in China can be improved by injecting foam agent. But in terms of the deep and high-pressure heavy oil reservoirs, the foam stability is poor when the saturated steam temperature is over 300 °C. Key words: steam drive, foam agent, thermal stability, thermal degradation rate, heavy oil recovery