With its high brightness and high collimation, the application of synchrotron radiation micro-infrared spectroscopy in polycrystalline diamond can significantly improve the accuracy of the analysis of nitrogen concentration and the residence time in the mantle. The results of synchrotron radiation micro-infrared mapping of the polycrystalline diamond demonstrated that nitrogen impurity in the sample had high content (500～1 300 μg·g-1) and high aggregation, which indicated that the diamonds from western Yangtze craton are type IaAB. The residence time in mantle of the sample was between 0.06 to 0.12 Ga. In general, the sample had different growth zones and multiple diamond grains which crystallize early respectively and aggregate later. In addition, some of the grains briefly ceased to grow during the polycrystalline diamond formation which formed in a volatile material situation.