The function of capillary pressure in the process of CO2 displacement in low-permeability reservoir is researched through combination indoor experiments and numerical simulation. On the basis of different displacement experiments in long core chamber, one-dimensional numerical simulation component model is built to research the function of capillary pressure under the different CO2 displacement ways. The results show that the capillary pressure under the different CO2 displacement ways is not consistent. Capillary pressure is driving force in the process of CO2 displacement while resistance force in the process of CO2 pressure buildup and displacement. In order to promote reasonable and efficient development of low-permeability reservoirs, it is suggested that further study about microscopic effects and laws of the capillary pressure in the reservoir should be done through experiment.