Abstract: The purpose of this research is to illuminate the connotation of the spectrum of the symmetrical narrow parts of the artery. The Doppler effect, the concise mechanism of the formation of the blood flow spectrum, the flow state which the spectrum of symmetrical narrow parts of the artery bases on, the distribution of its red blood cell mass, and some other knowledge are applied during the elaboration in order to achieve the expected goals. The three parameters that represent the dots on the blood flow spectrum, the relationships between the tandem dots at anytime and the detected blood flow state at that time, and the relationships between the blood flow state and the distribution of the red blood cell mass of it are illuminated. The connotation of the spectrum of the symmetrical narrow parts of the artery in the brain is reasonably elaborated. The conclusion that researchers should follow four steps in order to analysis the blood flow spectrum is reached in the end of the essay.

Key words: Doppler ultrasound, spectrum of the blood flow, red blood cell mass, the connotation of the vortex detected on the spectrum