On-line monitoring for identification gases is one of the most important goals in industrial production processes and safety warning areas. Compared with laser absorption spectroscopy, conventional monitoring methods are insufficient in terms of response speed, measurement accuracy, service life, real-time monitoring of a variety of monitoring targets, measuring range, and application scope. In this study, Tunable Diode Laser Absorption Spectroscopy (TDLAS) with an appropriate absorption wavelength was introduced and used for different applications: extraction method of industrial pipeline gases, in situ on-line opposite-type installation, diffusion probe method (integrated machine, multi-point passive transducer), and unstructured open-path monitoring. The detailed measurement results are as follows: The extraction system can be used to measure the concentrations of various gases, such as CO, CO2, and O2; Conventional O2 concentration and CO with a concentration less than 10 μL/L are measured based on the opposite-type system; The integrated machine and multi-point system uses CH4 measurement as an example to realize a response time T90=15 s, a monitoring limit less than 150 μL/L and a leakage alarm accuracy rate approaching 100%. Lastly, CH4/C2H2/C2H4 was selected to test the ability of the open-path system, which realizes an early warning ability of zero misstatements. According to long-time operation results, it is apparent that the TDLAS instrument is reliable, practical, and effective when applied to monitoring marking gases of industrial and mining safety production, and early safety warning.