There is an increasing need in many fields for fast, sensitive, and selective gas detection based on laser spectroscopy with the development of society. Quantum-cascade lasers are ideal light sources with its special characteristics of power, tuning and capability of operating in or near room-temperature. Quantumcascade lasers and a typical mid-infrared laser spectrometer based on a room-temperature distributed-feedback pulsed QC laser are described in detail, and the bright future of QC lasers used in gas detection is also showed.