Fire related gas sensing technology has been used to fire detection and has been regarded as a promising way for early fire warning, especially the optical absorption based gas-sensing. It can offer high sensitivity, low false alarm rates and early fire warning. A tunable diode laser absorption spectroscopy based fire gas detection system has been developed. The system used fiber-coupled near-infrared telecommunication distributed feedback (DFB) tunable diode laser as light source. Simultaneous detection of the two most common fire gas products, CO and CO2, was realized by modulation frequency multiplexed dual diode lasers. The system minimum detection limit for CO was estimated to be 0.00375 mg/m3 (3σ), and can meet the demands of in situ measurements of fire related gases.