A kind of particular rock type “leopard limestone” is widely distributed over Middle Permian Qixia Formation in the Northwest of Sichuan Basin. Based on the lithologic characteristics and micro-area and multi-parameter experimental analysis of samples taken from outcrops and drilling cores, the authors study the characteristics and genesis of the leopard limestone. The authors think that the leopard limestone consists of porphyritic dolomite and host bioclastic limestone. After exposure, the bioclastic limestone suffered karstification and the formed fracture-cavity system controlled the distributed pattern. The “leopard limestone” could be caused by the dolomization fluid from bottom to top, because at the end of the migration pathway, porphyritic dolomite was formed by metasomasis. Dolomization happened after consolidation diagenesis, the buried depth was shallow, and the origin fluid of dolomization could have something to do with hydrothermal fluids.