Age and distribution of the Middle Ordovician Shihtzupu(Shizipu) and Guniutan Formations have been researched based on large amount of conodont data and observations of field trips. It shows that the Late Darriwilian Shihtzupu Formation (Dw3) is dominated by shale and has a banding distribution along west—east direction including areas of northern Guizhou, southeastern Sichuan and northeastern Yunnan. The Guniutan Formation dominated by limestone could be classified into four types according to the characteristics of underlying and overlying strata. Both the base and tope boundaries of it are apparently diachronous. The age of base is between the late of Dw1 and the early of Dw2 corresponding to conodont Lenodus antivariabilis and Lenodus variabilis biozones. The top is from the late of Dw1 to that of Dw3, the latter corresponds to conodont Pygodus anserinus biozone. This formation mainly exists in eastern Sicuan, most of Chongqing, northern to northeastern Guizhou, western Hubei and northwestern Hunan. The upper part of the Guniutan formation could be correlated with the Shihtzupu Formation in part of these areas.