In this study, the human pathologic calcification samples were selected from human heart valve, artery, thyroid, ovarian and breast. Focusing on 38 cases of five different types, the authors carried out a systematic infrared spectrum characterization and, with the help of infrared spectrum method, inferred the presence of the carbonate group and evaluated the carbonate substitution in bioapatite structure. It was found that the basic composition of the five kinds of typical pathologic calcification product was carbonate-hydroxylapatite (CHA). The carbonate content of the samples in the same part remained the same,but the differences of the average content of the carbonate in different parts were obvious. The average content of CO₃^2- in the thyroid as well as the breast was 6.2, 3.3% lower than that in the heart valve. The average content of CO₃^2- in the heart valves was the highest. The infrared spectra showed that the pathological bioapatite mainly was the B-type carbonate substitution (CO₃^2- for PO₄^3-), accompanied by a small amount of A-type carbonate substitution (CO₃^2- for OH^-). The forward contact of the carbonate content inferred by the spectroscopic measurements and the ratio of B/A substitution was unconspicuous.