Sinter strength is mainly dependent on strength of iron-bearing minerals, bonding phase itself and bonding strength between bonding phase and iron-bearing minerals. Research indicates that the bonding strength between bonding phase and iron-bearing minerals is the major dependent factort of sinter strength. The ratio of bonding strength to sinter bonding strength meeting production requirements (12.58 MPa) is defined as bonding strength characteristic number to evaluate sinter strength. At the same time, the sinter strength is studied based on sinter microstructure. The results show that, compared with the microstructure of bonding phase itself, that of the interface between bonding phase and iron-bearing minerals is looser, on the other hand, due to the different cold contraction coefficient of solid and liquid phases, the internal stress is easily formed between bonding phase and iron-bearing minerals, which is not conducive to the improvement of bonding strength. Therefore, when bonding strength meets certain requirements, sinter strength can meet production requirements.