Laser tweezers Raman spectroscopy and singular value decomposition are used to explore the synthesis dynamics of biodegradable plastic poly- β- hydroxybutyrate(PHB) in C. necator H16 strain cultured with different nitrogen sources at the single- cell level. The results show that ammonium sulfate performing best on fermentation speed, efficiency and productivity in all tested nitrogen sources, is demonstrated as an ideal nitrogen source for PHB fermentation. The singular value decomposition results reveal that the main fermentation features are the Raman peaks belonging to RNA, DNA, protein and PHB, and the difference in bacterial cells and product yield becomes more notable as the fermentation process works. The dynamics of Raman intensity peaks of nucleic acid, protein and PHB at 782, 1574, 1660, 1732 cm^-1 are active to the fast PHB synthesis, and no matter what nitrogen sources are used, the intensity of peaks at 1660 cm^-1 and 782 cm^-1 is positively correlated, but the intensity of 1660 cm^-1 and 1732 cm- 1 peaks is negatively correlated. The results suggest that nitrogen sources influence the RNA and the protein metabolism and then affect the synthesis of PHB indirectly. Raman spectroscopy combining with data analysis can provide the metabolism information of the microbial fermentation and offer a powerful experiment basis for optimizing fermentation process.