The presence and porosity of pores in pellets have a very important influence on the performances of pellets. At present, the methods for detecting the porosity of pellets are mercury pressure method, SEM image recognition method and X-ray computed tomography (CT) method. In order to clarify the advantages and disadvantages of the three detection methods and accurately obtain the porosity of pellets, the relevant comparative tests are carried out based on on-site pellets 1^# and 2^#, and the relationship between the three-dimensional pore structure characterization and performances of pellets is elaborated. The analysis results show that the mercury pressure method cannot detect the closed pores, the SEM image recognition method can only detect local pores, and the CT scanning method can reproduce the internal pore distribution state of pellets, which is a relatively complete pore detection method. The characterization of pore structure can more concretely analyze the changes of compressive strength and metallurgical properties of pellets, such as the compressive strength of 1^# pellets with more internal pores and most of them in the form of connected pores is lower than that of 2^# pellets with fewer internal pores and most of them in the form of closed pores, and the reduction performance of 1# pellets is better than that of 2^# pellets because the connected pores are conducive to the transfer of reducing gases.