The mineral assemblage of impure carbonate rocks is closely connected with the total pressure and partial pressure of CO_2. The production temperature of tremolite, diopside and olivine is raised with the rising of total pressure. There are two extreme types of fluid behavior during metamorphism, i.e. infiltration and buffering. During infiltration metamorphic reaction takes place at certain determined temperature and all reactions will occur discontinuosly. All mineral assemblages in closely spaced outcrops are stable at same partial pressure of CO_2. The point of infiltration metamorphism on TX_(co_2) diagram is rarely on the reaction curve. In the field there is no abrupt boundary between different mineral assemblages. Minerals controlled by infiltration metamorphism are enriched or deprived in some elements with uneven grain size and without inclusions. Based on above mentioned characteristics metamorphism controlled by buffering could be distinguished from metamorphism controlled by infiltration. The impure carbonate rocks of Susong Group, Hebei and Hongqiyingzi Group, Hebei are metamorphosed under infiltration. The impure dolostone of Banyukou Formation, Wutai Group, Shanxi is metamorphosed by combination of infiltration and buffering.