Abstract: For esterification of free fatty acid in high acid value Jatropha curccas L.seed oil with methanol,ST (SO42-/TiO2) solid acid prepared by directly calcining cheap industrial metatitanic acid has high activity.FTIR studies suggested that ST solid acid possessed pyrosulfate structure with high bond order and high covalent S=O.The intensive inductive effect of S=O made the neighboring unsaturated coordinated titanium atom to have strong Lewis acidity,which converted protonic acidic sites when the catalyst absorbed water.The protonic acidity increased with the S content increasing.During preparing ST solid acid,the sulfate was effectively binded to the titania surface through the solid phase reaction of sulfate with titania.At the same time,SO3 generated by decomposition of partial sulfate was absorbed in situ and formed solid acid structure.The strong acid site increased and the weak acid site decreased with the calcination temperature increasing.Since the surface sulfate decomposed at higher calcination temperature,the amount and strength of acid site deceased sharply,which induced the decreasing of the esterification activity of the ST solid acid.For the esterification of free fatty acid in high acid value Jatropha curccas L.oil with methanol,the acid site in H0 between-12.70 and-8.2 has better catalytic activity.The ST solid acid catalysed esterification proceeds through a reaction routine of protonating fatty acid,which conducts nucleophilic addition with methanol and then deprotonating.