Objectives: Maoping and Huize Pb—Zn deposits in Yunnan Province are important parts of carbonate type Pb—Zn metallogenic domain in Sichuan, Yunnan and Guizhou, and are the two most representative super-large deposits in northeast Yunnan Pb—Zn concentration area. The lenticular and cystic alteration near the lead—zinc ore body is commonly known as “mottling rock” because of its mottling-like appearance, which is accompanied by faults and mineralization in space, and is an important prospecting sign. Methods: In this paper, mottling altered wall rock is taken as the main research object, the material composition, fabric characteristics and formation process were studied by fine measurement of large-scale tunnel section, petrographic analysis, electron probe analysis, X-ray micro-area diffraction analysis and principal and trace element analysis. Results: According to the fabric characteristics, altered wall rock can be divided into two categories. the type-Ⅰ altered wall rock is saccharoidal, and the mineral particles are mainly dolomite and calcite with coarse crystalline structure (0.5~1 mm), which are cemented by clay minerals such as brown illite; the type-Ⅱ altered wall rock is mottled, and the mineral particles are mainly calcite and dolomite with giant crystal texture (1~3 mm), which are obviously recrystallized and cemented by black argillaceous and organic matter. Through hand specimen observation, microscopic identification and comprehensive analysis, the type-Ⅰ altered wall rock is named as weakly marbled coarse-grained argillaceous dolostone, and the type-Ⅱ altered wall rock is named as dedolomitized giant crystalline limestone. Compared with the major element characteristics of the two types of altered wall rock, the content of SiO2, Al2O3 and K2O in type-Ⅰ is higher. The trace element characteristics show that the main mineralized elements (Zn, Pb) are enriched in the two kinds of altered wall rock. The REE characteristics show that the REE contents in weakly marbled coarse-grained argillaceous dolostone (type-Ⅰ) are higher than that of dedolomitized giant crystalline limestone (type-Ⅱ), and the REE characteristics of dedolomitized giant crystalline limestone (type-Ⅱ) are similar to those of mineralized dolomite. Conclusions: Two types of altered wall rock are products of different stages of the same fluid system, and their diagenesis models are constructed: the original rock of weakly marbled coarse-grained argillaceous dolomite (type-Ⅰ) is calcareous mudstone, and high-salinity brine seeps down, which reacts with mudstone and dolomite at the lithologic interface to form argillaceous dolomite. After the sedimentation is stable, due to the influence of tectonic movement, hydrothermal fluid rises along the fault, and argillaceous dolomite marmalization is formed in favorable sections (structural change). Dedolomitized giant crystalline limestone (type-Ⅱ) is more strongly altered than the weakly marbled coarse-grained argillaceous dolostone (type-Ⅰ), which has undergone mineralization, marbling and dedolomitization. The comprehensive analysis shows that there is a close genetic relationship between altered wall rock and lead—zinc ore bodies in terms of time, space, ore-forming materials and ore-forming fluids, etc. It is suggested that the marbling and dedolomitization have important indicative significance for the ore-forming and ore-prospecting of this type of deposit.