Abstract: In order to improve the hydrophilicity of humic acid,the lignite humic acid was modified by sulfonated method.Taking Na2SO3 as sulfonatingagent,sulfonation degree as index,the influence of humic acid-sulfonating agent ratio,reaction time,temperature on acid sulfonation degree was studied through the single factor experiment and orthogonal design method.The authors got the optimum preparation condition,meanwhile,characterized the humic acid through infrared spectrum analysis and thermogravimetric analysis(TGA).The results showed that,the reaction temperature was the main influencing factor,followed by reaction time,humic acid-sulfonating agent ratio.When the sulfonating agent-humic acid ratio was 2 to 20,the sulfonation temperature was 50 ℃,the reaction time was 90 minutes,the sulfonation degree was 17.72%.The IR spectra showed that the modified humic acid contained benzene ring,carboxyl,hydroxyl,phenolic hydroxyl group.Its sulfo groups increased significantly.The TGA showed that,the sulfonatedhumic acid was stable when the temperature was lower than 200 ℃,while the temperature was higher than 200 ℃,the sulfonatedhumic acid began to deposit.When the temperature was lower than 330 ℃,the deposition was endothermic reaction,otherwise,the deposition was exothermic reaction.