Most major diamond deposits are located in North China Craton (NCC). Recently large number of microdiamonds from alkalic basic rocks were discovered in south of NCC (in northen Jiangsu & Anhui provinces). These are new type of diamonds that differ from the kimberlite and lamproite types. In this research, these diamonds were tested and analyzed by FTIR. Most diamonds contain isolated nitrogen (C center), while a few contain nitrogen pairs (A centers) and nitrogen aggregates (B centers), in which Y center (1145~1150 cm -1) is associated with C center, indicating that these diamonds are mostly of natural Ib, Ib/IaA and IaAB types, of which Ib is the dominant type. Nitrogen is the most common substitutional impurity in diamonds and is present in numerous combinations of nitrogen±vacancy centres. The content of N in diamonds from this area is generally not high. From the calculation of IaAB diamond’s FTIR data, it is believed that the mantle residence time of the IaAB diamond is about 550 Ma, the temperature recorded by the diamond is about 1225 ℃ and is derived from a depth of 150 km. The large number of Ib type diamonds from this area indicated that the diamonds were rapidly uplifted from the diamond stability field when they were still “young”, so most of isolated nitrogen was preserved and not aggregated to A centers.