Spirulina, Spirulina powder and dextrin standard were analyzed and identified by Infrared (IR) spectroscopy. The main components, protein(1 657 and 1 537 cm-1) and carbohydrate(1 069 and 1054 cm-1), had distinct fingerprint characteristics of IR spectra. By comparing the IR spectra of Spirulina, Spirulina powder and dextrin standard, the dominant nutrition in Spirulina powder was identified as protein and carbohydrate. The dominant accessory added in Spirulina powder was dextrin. Comparing the IR spectra of Spirulina powder from 28 different factories and figuring out the correlation provides the information about the amount of accessory. A standard curve of the ratio of absorption peak intensities to protein content was constructed to accurately determine the amount of protein in Spirulina powder.