Abstract: For better prevention of spontaneous fire in gobs affected by water immersion,variation on the microstructure and spontaneous combustion characteristics of Bulianta and Xiqu coal before and after long-term water immersion were investigated by detection techniques such as DSC,FTIR,XRD etc. Results showed that after 30 -90 d immersion the activation energy de-creased 1. 73-7. 94 kJ / mol,and the heat release rate of coal samples in the process of low tem-perature oxidation were increased. And the absorption peaks of —CH2—,—OH,C—O etc. changed significantly. Be-sides,after long-term water immersion,mineral elements Si,Na,Ca,Fe,S etc. gathered on coal surface. Meanwhile, SiO2 content in coal was sharply reduced,which resulted in the treated coal swelled and broken continuously. Micro-pores ( >10 nm) also enlarged 4. 61% -17. 35% in treated coal,which increased the oxygen diffusion rate. Due to the tensile strength of treated coal dropped to 0. 192-0. 495 MPa,block coal can more easily break into fine coal with dif-ferent particle sizes,which increased the risk of spontaneous fire in goaf. In comparison,after water immersion,the change of self ignite characteristics in Bulianta coal is stronger than that in Xiqu coal,which could be attributed to the differences in the minerals composition and content of coal.