In this paper,a vehicle-mounted fire emergency rescue multi-gas monitor based on DOAS (Differential Optical Absorption Spectra) technology is reported,which can continuously monitor more than 30kinds of poisonous gases.A long path ultraviolet differential absorption spectroscopy method for trace gas analysis is used to realize the continuous monitoring the gas components and the concentrations in the air.Optical transmitter and optical receiver share a Cassegrain telescope,in order that the atmospheric turbulence effects on the measurement data can be reduced.Reflection system can be set in any measurement area flexibly,and analytical system is set in the rescue vehicle,which can avoid the rescue worker exposure in dangerous environment at close range when continuous monitoring is required.Multi-gas DOAS system is especially suitable for fire emergency treatment of various gas leakage accidents.