Abstract: Applying thermo-elastic-plastic model and finite element software,this paper simulated underground gasification of coal.Stress field distribution and plastic area distribution of overlying strata was obtained in gasification.Results showed that there was arch structure over gob and inside of the arch was caving and fissure zone.With the face advanced,stress concentration occurred before and after the coal wall and stress concentration range extended increasingly,stress summit increased as well,plastic area of overlying strata extended and when plastic area connected with each other,overlying strata would cave wholly and this might reached surface.