According to the characteristics of high bottom hole temperature and large temperature difference between the inner and outer walls of reservoir casing in the process of underground coal gasification (underground coal gasification), the temperature field and stress field model of wellbore in gas production wells is established based on thermo-mechanical coupling, and the stress distribution of different steel grades of casing under limit working conditions is studied. The results show that: (1) under the condition of daily gas production rate of 30×10⁴m³/d and gasifier temperature of 1000°C, P110 steel grade casing always meets the strength requirement; N80/L80 steel casing yielded at 188°C, and the critical gas temperature of J55 steel casing was 990°C after cooling by spraying device. (2) J55 steel grade casing can be selected when the temperature of gasifier is lower than 600C, N80/L80 steel grade casing can be selected when the temperature is in the range of 600°C–900°C, and P110 steel grade casing can be selected when the temperature exceeds 900°C.