In the process of oil recovery with carbon dioxide injection，carbonic acid is formed when carbon dioxide dissolves in water，which reacts with reservoir minerals，and the mineral composition of rock and physical properties of reservoir are changed. In this paper，the changes of minerals，producing fluids，microstructure and permeability of low permeability reservoir under three different injection methods of CO₂ flooding，alternate CO₂/waterflooding and CO₂ huff-and-puff were studied by laboratory experiments. The results showed that the core permeability could be increased by these three CO₂ injection methods to some degree. Among them，alternate CO₂/water flooding had the most obvious effect on the core permeability，the concentration of calcium and sodium ions of the producing fluids increased obviously and the dissolution of carbonic acid resulted in the reduction of plagioclase and calcite in the core so that the content of calcite and feldspar in the core mineral decreased. The original microstructure of rocks was dense，and the core possessed poor connectivity and poor development of intergranular pores. After the effect of carbonic acid， the microstructure of rocks was loose，and the core possessed good connectivity，well-developed intergranular pores and obvious dissolution.