The sinter pot experiment method is used to study the influence of basicity (0.6 ~ 2.4) on sinter drum strength, and the internal mechanism of formation of strength-basicity low-concave area are analyzed from the perspective of mineral composition and microstructure. The research results show that, when the basicity is 0.6 ~ 2.4, with the basicity increasing, the sinter strength substantially first reduces and then rises, and the strength-basicity low-concave area appears in the vicinity of 1.6. The main reason is that, when the basicity is in the vicinity of 1.6, the content of the effective binder phase (calcium ferrite) is low, the mineral composition is complex and mineralogical structure shows coexistence of mixed corrosion structure - part porphyritic texture - local granular structure and the structure is extremely inhomogeneous. When the sinter is cooled, the internal stress will lead to formation of large number of cracks and the strength is low, thus the strength-basicity low concave area appears.