Using FTIR, SEM and EDS, the authors systematically studied the mineral composition, micro-characteristics and the variation of chemical composition of the weathered layer of Changhua secondary dickite stone, which is usually called Changhua Tianhuang. The result indicates that the main mineral composition of the weathered layer is kaolinite-group minerals, consisting of some Fe, Ca, Mg-bearing accessory minerals. Compared with those of the inner layer, the mineral crystals of the surface weathered layer have a blurred boundary and shape, due to the dissolution and the filling of Fe-bearing minerals. The difference of micro-characteristics between inner and surface layer as well as the decreasing of Fe, Ca from weathered layer to unweathered layer demonstrates the weathered progress of the Changhua secondary dickite stone. The appearance of quartz in the weathered layer and the attachment of the Mn-bearing mineral can help identify the origin of Changhua and Shoushan Tianhuang stone.