Abstract: In order to study the effect of pH value of mine water on the spontaneous combustion characteristics of residual coal in goaf, long-flame coal from Pingdingshan Coal Mine was used to analyze the gas production law and heat flow curves of gas derived from low-temperature oxidation stage by using C600 high-precision microcalorimeter and gas chromatograph. Based on the experimental results, the microscopic mechanism was discussed. The results show that soaking in acidic aqueous solution significantly promotes the oxidation property of coal, and the higher the acidity, the greater the impact, while the soaking in alkaline aqueous solution inhibits the oxidation property of coal sample. It is concluded that the reaction between acid solution and minerals in coal may increase the porosity of coal and promote the process of spontaneous combustion of coal. The reaction of alkaline solution with coal sample produced sediment, which inhibited the spontaneous combustion reaction of coal to a certain extent.