The CO₂ fluids and volcanic clastic rocks chosen from Nanbeier Depression were studied experimentally at different temperatures(100, 120, 140, 160 and 180℃). The results show that the corrosion intensity of feldspar and calcite will be enhanced gradually with the increasing temperature, but the dissolution degree of quartz is very low. The tuffaceous material can be dissolved by CO₂ fluids, and it seems to be the main dissolution object of CO₂ fluids. Chlorite and boehmite were found on the surface of the sedimentary tuff sample at the temperature of 160℃ by scanning electronic microscope (SEM). Considering that there are a good many carbonate minerals (especially dawsonite) and secondary solution pores in Tamtsag Basin, the authors hold that the CO₂ fluids have made considerable contribution to the formation of secondary pores in Tamtsag Basin.