Abstract: Dolomites of the Penglaiba Formation in Yubei area were divided into fine-crystalline matrix dolomites, coarse-crystalline matrix dolomites and saddle dolomite fillings according to the petrographic features. The saddle dolomite fillings have geochemical features similar to the coarse-crystalline matrix dolomites. They appear to be dolomite cements, and are not associated with limestone replacement. Diagenetic fluids for saddle dolomite fillings are inferred to be high-temperature and high-salinity formation brines. The average Sr content of fine-crystalline matrix dolomites is higher than that of coarse-crystalline matrix dolomites and saddle dolomite fillings, while the average Ba content of saddle dolomite fillings is much higher than that of matrix dolomites and coarse-crystalline matrix dolomites. The Mg/Ca ratios of fine-crystalline matrix dolomites, coarse-crystalline matrix dolomites and saddle dolomite fillings are similar. The REE distribution curves of saddle dolomite fillings and matrix dolomites are similar. The inclusion analyses of coarse-crystalline matrix dolomites and saddle dolomite fillings show overlapping fluid properties, which indicates that saddle dolomite fillings are inherited from matrix dolomites.