Abstract: Dajingtou pluton is the first diamondiferous lamproite discovered in the west of Tan-Lu fault zone. This paper studies the laser Raman and Fourier transform infrared spectra(FTIR) of the diamonds.The laser Raman and infrared spectrum data shows that the six diamonds from the Dajingtou lamproite can be distinguished into type Ia and type Ib. Some of the type Ib diamonds are superimposed on the type 1a with 1175 cm^-1 or 1182 cm^-1 absorption spectrum,which are unique to type Ia diamonds. According to the appearance features of the six tested diamonds and the conversion mechanism of type Ib to Type Ia, it is considered that diamonds in Dajingtou lamproite are not the cause of magma crystallization, but the mantle-derived xenocrysts, which were first formed in the mantle and then carried to the surface by ultra-deep magma. Taking into consideration of the excellent geological tectonic conditions, the abnormal heavy sand minerals in the diamonds, and the exposure of ultrabasic rocks and volcanic breccia, it is believed that this area is expected to be the fourth primary diamond belt in western Shandong.