In this study, pyridine_Raman spectrometry was used to study surface acid site properties of diatomite. In the experiment,the surface hydroxyl groups could not play the role of Brφnsted acid sites without thermal treatment because they were all covered with water molecules,and there appeared no Lewis acid sites either. After being heated, some B acid sites appeared on diatomite surface,which originated from the surface acid hydroxyl groups that had desorbed water molecules, and the B acid sites reached the maximum quantity after being heated at some 650℃. Under the same treatment condition, L acid sites also appeared, and this was attributed to the structural deformation of clay minerals in diatomite.