Abstract: A study of the nature of the protoliths of metamorphic rocks in the Tuolai Group and their tectonic setting shows that the schist, gneiss, quartzite and marble in metamorphic rocks of the Tuolai Group are originally sedimentary rocks, and the amphibolite in metamorphic rocks of the Tuolai Group is basic volcanic rock. The protolith of schist and gneiss is greywacke, the quartzite is quartz sandstone, the marble is dolostone and limestone, and the amphibolite is basaltic andesite. Discrimination of the tectonic setting of meta-volcanic rock indicates that the amphibolite formed in an intracontinental rift environment. As the special interlayer of Tuolai Group, the metasedimentary rocks should have the same tectonic environment as the anphibolite, both formed in an extensional basin.