Fire accidents often cause unpredictable catastrophic losses. At present, existing fire prevention measures in public places are mostly based on the emergency treatments after the fire, which have limited protection capability when the fire spreads rapidly, especially for the flammable liquid explosion accident. Based on the gas sensor network, this paper proposes a detection framework as well as detail technologies to detect flammable liquid existing in small spaces. We propose to use sensor network to detect the flammable liquids through monitoring the concentrations of the target liquid vapor diffused in the air. Experiment results show that, the proposed surveillant system can detect the gasoline components in small space with high sensitivity while maintaining very low false detection rates to external interferences.