In the fiber-sensing gas detection system, characteristic of near infrared absorption spectrum of the detected gas is greatly significant. The volatilized gasoline vapor is a mixture rich in various components, of which near infrared absorption spectrum shall be determined by means of experimental measurement. In this paper, an experimental platform is constructed by analyzing absorption characteristic of liquid composition in gasoline within the range of near infrared spectrum, which achieves measurement of the volatilized gasoline vapor with different concentration. In addition, reliability of this measurement method is inspected, a comparison between features of absorption spectrograms of liquid and gas is made, and linear relation of absorbance and concentration of gasoline vapor is verified. The result shows that the experimental data is acceptable and may be used as the basis of further analysis and for design of the online detecting system of gasoline vapor concentration in the hazardous environment.