Abstract: Based on the analysis of carbon dioxide(CO₂)produced by the thermal hydrolysis modelling experiment of three sorts of calcium-bearing carbonate(CaCO₃)source rocks,the genesis of carbon dioxide(CO₂)in the gaseous products is approached.There exists both organic and inorganic genesis.The higher the content of calcium carbonate and the finer the grains of rocks,the higher the yield of inorganic carbon dioxide.The generation of inorganic carbon dioxide restrains the organic material of calcium-bearing carbonate source rocks from producing hydrocarbons at some degree.