Blue coral is a rare coral species. Previous studies have confirmed that the color of blue coral is related to biliverin from a biological point of view. Still, there is no relevant spectral evidence and a lack of microstructure studies, so the explanation for the color of blue coral is murky. Based on this, according to the absorption band of the infrared transmission spectrum of blue coral from 4 000 to 2 000 cm^-1, this paper shows that blue coral contains certain organic matter, and the organic matter content is positively correlated with the color depth. The characteristic Raman peaks of biliverdin were found at 1 616, 1 542, 1 459, 1 356, 1 314, 1 264, 1 167 and 970 cm^-1 in the blue region of blue coral. The absorption bands in the UV-VIS spectra of 286, 357, and 590 nm are also consistent with the absorption bands of biliverdin. The above spectral characteristics indicate that the blue color of blue coral is related to biliverdin. Secondly, the micromorphologic characteristics and composition analysis of blue coral showed that the pores formed by blue coral polyps were approximately parallel longitudinally, and the holes were superimposed in segments. From the inner surface of the pores (spiniform aragonite) to the periphery of the pores (lamellar aragonite) to between the pores (columnar aragonite), the content of organic matter decreases significantly as the color changes from blue to white. Combined with the previous research results, it can be inferred that the exudation of keratin and calcareous substance from the ectoderm of polyps forms the white aragonite between the pores. After the polyps die, the endoderm and the nematocytes on the surface of the endoderm become fossilized, preserving the organic matter in the polyps, which contains biliverdin, causing the blue color of the blue coral.